My realization that smoking was associative, led me to try to do it alone. I told everyone in my social circle that i had quit, and smoked in secret when I had to. I don't generally espouse lying but it might be a prerequisite in this case. I stopped using smoking as an aid to social situations, or as something to do with my hands and mouth when i was pensive. I focused completely on the very process and did not accompany smoking with anything else at all. What this method encompasses is, being very aware of smoking, from lighting it, putting it on your lips, inhaling the smoke, exhaling, to flicking the ash and throwing the butt away. I also focused on the sensations in my mouth and lungs, as well as the blood rush. It reduced my daily intake immediately, made me despise smoking, and along with other measures, helped me kick the addiction for good.

I was always wary of using drugs to solve my problems (I always thought I should just apply more willpower), but then my anxiety got so bad that I cried every day for nearly a year. Going on SSRIs immediately made a massive difference. I only cry about once a month now and have far more good days than bad.

Similarly, sucking it up and taking ibuprofen when I feel a migraine starting is way better than 'powering through' it. You requested only one problem-solution pair per answer, so I'll generalize this to 'significant life improvements when I stopped blindly rejecting drugs on principle.'

I used to have really strong emotions that could be triggered by trivial things, which caused both me and the people I was around a lot of suffering.

I managed to permanently stop this, reducing my emotional suffering by about 90%! I did this by resolving to completely own and deal with my emotions myself, and told relevant people about this commitment. Then I was just pretty miserable and lonely feeling for about 3 months, and then these emotional reactions just stopped completely without any additional effort. I think I permanently lowered my level of neuroticism by doing this.

I frequently got trapped browsing the internet on my phone, so I removed the web browser from my phone. You would think that I would just reinstall the browser, but adding 5 extra seconds delay is apparently sufficient for me to have impulse control.

I grew up in warm climates and tend to suffer a lot in cold weather. I moved to a colder climate a few years ago and discovered scarves. Wearing scarves eliminated 90% of this suffering. Scarves are not exactly a bold and novel invention, but people from warm climates may underestimate their power.

Writing down ten ideas a day. This "exercise" of my idea muscle, with just a few months, completely rewired my brain to start thinking more creatively.

I was using my phone too much in bed, so I moved my phone charger far enough that it wouldn't reach my bed.

Setting a recurring alarm at 9:30pm and taking melatonin right away. Got me in the habit of getting tired and going to bed more consistently.

I discovered a year ago something that substantially improves my mood and energy. In the shower each morning, I rub the sole of each foot for just a few seconds with a facecloth (or anything slightly rough would do). This produces a buzz (kinda endorphins + caffeine) that lasts all day, without wearing off as it is renewed by standing or walking. It hasn't diminished over time. It's an amazing free lunch. Not just making life 0.1% better, I'd genuinely say 30% better.

Perhaps I have particularly sensitive feet. But presumably this works for some other people, they just haven't tried it; after all, it took me decades to discover it.

Problem:
Regularly eating unhealthy snacks/food.

One-time solution:
Put all the unhealthy snacks/food in a hard to reach shelf in the pantry, and shove them all the way to the back.

Notes:
This solution is very effective in reducing the snacking and junk-food eating. It's based on two laws of behaviour change${}^{\ast }$.

1. Make it Invisible: If it's out of sight, it's out of mind. With the junk food tucked away, you'll be tempted a lot less, if not completely forget that those foods were even an option.
2. Make it Difficult: Bending all the way down to reach into the bottom shelf of the pantry (for me, that's at floor level) is really tedious, and that bit of resistance is surprisingly effective in reducing my desire to get that snack/food.

Bonus point — A similar trick is actually well-known in retail: whatever product you put in the top shelf (waist-height) near the cashier will sell much more than any product you put in the bottom shelf (even if the bottom product is a much better-known brand).

* These laws come from the book Atomic Habits, which I've read twice and have grokked fully. As a result, I was able to easily come up with dozens of these one-time solutions for all my daily problems. I consider it a life-changing book and I highly recommend it (and I'd love to chat with anyone about habit design, just PM me).

Problem: Binge-watching youtube videos.

Solution: A browser extension that removes the recommended videos sidebar.

This has easily saved me tens of hours of wasted time.

I only started doing cardio consistently once I paid the upfront cost of trying 14 different pairs of shoes till I found some that made my feet hurt less.

Getting rid of all but ~100 belongings permanently decreased how much time I spend cleaning since the worst things ever get still only takes 10 minutes.

Learning to make 3-4 meals, not in the sense of 'I know the procedure' but in the sense of 'I buy these specific things at these specific stores in these specific quantities and follow this exact procedure each time' ingrained it into muscle memory enough that it no longer occurs as aversive.

Buying a Reach Access flosser made me floss.

Practicing the muscle memory of opening a new note in my favored note taking app and reducing the number of buttons I need to press to do so eventually bootstrapped to a very robust note taking system.

Problem:
Endless watching of Netflix (or Youtube).

One-time solution: 
Disable auto-play on Netflix (it's a config setting, which applies across all devices).

Notes: 
Auto-play on services like Netflix is extremely dangerous, especially when watching TV shows whose plot advances episode to episode as if it's a really long movie. For me, watching videos is really immersive and induces a flow state, which famously causes time to dilate (in this case, it shrinks). Hence, without a clear signal that a "unit" of watching has completed, I would get stuck watching for hours at a time.

Additionally, the tiniest bit of resistance (i.e. having to reach for the controller/mouse to click the "Continue" button) seems to be just enough to allow me to regain a semblance of control.

Finally, I instituted a rule for myself: I can watch as much Netflix as I like, provided that before I click the "Continue" button, I must do at least 1 productive thing. Interestingly, most nights, after watching a single episode, I end up stuck in a flow state doing the productive thing instead and the whole evening turns out great!

Installing freedom.to, which lets me deactivate websites that are distracting, and sync them acros devices. (I previously tried various things to add a delay to particular websites, not of which worked nearly as well)

I think for Freedom to work, it needed me to also have an active project I was working on that I actually enjoyed. I think otherwise I would have found other ways to distract myself and eventually undermined it to the point that I gave up.

A friend tells me that they would have a new cold sore every ~3 weeks during winter months. After reading this paper: https://proceedings.med.ucla.edu/wp-content/uploads/2016/03/A151218DG-WH-edited.pdf they told the local pharmacist that they needed the chickenpox vaccine since they never had it as a child (which was a lie). Since then (about 3 years), they have only had one cold sore which was much milder than the previously typical ones.

As a side note: it seems to me like it would be worth trying this as a pre-exposure prophylactic for genital herpes if you have sex with multiple people.

I frequently stayed up late on my computer. A timed outlet that turns off my monitor at 10pm almost completely solved this problem by forcing me to actively choose to continue using it.

Using duct tape to tape my floss to my toothpaste has moved my flossing compliance from ~80% -> ~98%

I had bad carpal tunnel pain and RSI due to my coding job 3 years ago, to the point where it was very painful to type, and moderately painful all the time. I was worried I would have to find a new career.

I solved it by seeing David Bacome at Psoas in SF. After about 7 sessions the pain went away completely. He also taught me how to do some exercises to help prevent it from happening again, which I do whenever I start feeling lots of tension in my wrists. It hasn't been an issue since then, and I have no problem using a keyboard for both work and many of my hobbies.

I replaced everything except the ceiling lights with no-blue lights and use F.lux on my devices. Now I get sleepy when I'm supposed to and never stay up late.

Getting up at the exact same time every day, unless I happen to wake up before my alarm goes off. It seems to have improved my sleep quality.

I started prioritizing my to do list each day by urgency+impact+ease, and I accepted the fact that time spent prioritizing is time very well spent.

Problem:
Spending too much time using your phone each day (surfing, messaging, watching videos, ..etc.).

Solution:
Change your phone's display settings to only display in grey scale.

Notes:
I saw this tip online a long time ago, and have tried it on several occasions to break an addiction to my phone (where I was glued to my phone for hours daily).

It's shocking how well this trick works. You realize after using your phone in this mode for a few days how effective colours are in getting and keeping your attention, all in the name of getting you more "engaged" with apps / your phone.

One the one hand, this one-time solution gets rid of all these temptations wholesale, on the other hand, it's almost nauseating to use the phone for a long period of time in grey scale. I don't know why, but I will literally end up tossing my phone away in disgust after a few minutes of using it in this mode, thereby very effectively solving the original problem.

Signing up for email from Superhuman. I went from "always have a pile of unchecked email, very bad responsiveness, feeling of overwhelm" to "I look forward to checking my email and inbox zero everyday effortlessly". 

The change happened basically immediately after the 1h onboarding session. 

This was actually a major update in how building software to reduce frictions can cause qualitative changes to my productivity.  

I could rave about superhuman for a long time, enough that this answer will just sound like an ad. But take it upon my karma and reputation as an LW user that it's just my genuine opinion. 

I spent a lot of time sitting, because computers are both my work and my hobby. I was thinking about solutions, and I had a few ideas, but I procrastinated for years.

Recently, a health problem made me look for a solution immediately. So I put a huge plastic box on my table, and put the monitor and keyboard on the top of the box, and now I use the computer while standing. At first it felt weird, and I quickly got tired. But after a few weeks, my body adapted and now it feels natural. And the health problem that inspired this change is mostly gone.

Another positive side effect is that the "activation energy" needed to leave the computer is much smaller when I am no longer sitting. Yet another is that my 2 years old daughter no longer tries to climb in my lap whenever I try using the computer.

From the rationality perspective, it is quite humiliating to notice how long it took me to finaly address a problem that could have serious health consequences, and how little time and effort the actual solution required, once the gun was metaphorically pointed at my head.

(To be honest, I am not completely satisfied with this solution, and would like to replace the plastic box with something better... not sure what exactly. But the difference is that now I procrastinate on minor improvements, having already solved the critical part.)

If it will take < 5 mins do it immediately.

It works for responding to e-mails, buying stuff for home, paying bills etc. Benefits which I noticed:

• It allowed me to have smaller backlog of quick task
• I feel I have less cluttered mind
• I feel I forget less stuff which I need to do

Problem: I had a lot of back pain. Some days I'd wake up in pain, and it wouldn't go away for 1-4 days afterwards. Almost once per week? No rhyme or reason.

Solution: Replace the blanket I was using to sleep. My blanket was too small, I would curl up too tightly to stay under it. Now I still very occasionally get the same problem, I'm guessing because of habits, but it's more like once every three months.

My glasses didn't fit properly, causing them to slide down my nose frequently. I used hot water to bend the frames around my ears better, solving the problem.

Glide floss. My teeth absolutely shred every other brand, but Glide is coated with Teflon. Made regular flossing possible.

I stopped watching news years ago. Improved my mental state massively.

Stretching every day, right after work, has been a win as well. It’s a good end to the day, I’m way more flexible, and overall feel happier.

Whenever I feel angry or frustrated, I ask myself what outcome I want from the situation, and focus on how to make that happen. Helps me avoid acting counterproductively on emotion.

1st problem: waking up on time/not going back to bed:

Moved my alarm clock into my office (which is situated right beside my bedroom). Forced me to get up, take a few steps, and consciously turn off the alarm. Since the closest place to rest was the office chair, I found myself not going back to bed and waking up on time with almost 100% compliance.

2nd problem: dishes

I don't have a dishwasher in my apartment, they all need to be done by hand. we (my partner and I) recently limited our cabinets to 4 of each item (cups, plates, bowls, cutlery) and the amount of dishes we need to do is now 90% less. We keep the other items in a closet incase we have company over.

Buying a pack of 5 phone chargers on Amazon. I didn't realize how nice it was to have two in my apartment, two in my car, and a dedicated travel charger until I spent $10 on it.

Buying my girlfriend a vape. She smokes weed a lot and it's been said that getting a smoker to switch to vaping is one of the best things that you can do in terms of longevity. She also says that it is much more enjoyable.

(She likes the Pax 3 a lot; Vape Critic seems like a good resource for reviews.)