This is a trick that I use for getting out of bed in the morning - quite literally: I count down from 10 and get out of bed after the "1".
It works because instead of deciding to get out of bed, I just have to decide to implement the plan to count down from 10 and then get out of bed. Once the plan is in motion, the final action no longer requires an effortful decision - that's the theory, anyway. And to start the plan doesn't require as much effort because I just have to think "10, 9..."
As usual with such things, there's no way to tell whether it works because it's based on any sort of realistic insight or if it works because I believe it works; and in fact this is one of those cases that blurs the boundary between the two.
The technique was originally inspired by reading some neurologist suggesting that what we have is not "free will" so much as "free won't": that is, frontal reflection is mainly good for suppressing the default mode of action, more than originating new actions.
Pondering that for a bit inspired the idea that - if the brain carries out certain plans by default - it might conserve willpower to first visualize a sequence of actions and try to 'mark' it as the default plan, and then lift the attention-of-decision that agonizes whether or not to do it, thus allowing that default to happen.
For the record, I can remember a time some years ago when I would have been all enthusiastic about this sort of thing, believing that I had discovered this incredible new technique that might revolutionize my whole daily life. Today, while I know that there are discoverables with that kind of power, I also know that it usually requires beginning from firmer foundations - reports of controlled experiments, a standard theory in the field, and maybe even math. On the scale of depth I now use, this sort of trick ranks as pretty shallow - and in fact I really do use it just for getting out of bed.
I offer this trick as an example of practical advice not backed by deep theories, of the sort that you can find on a hundred other productivity blogs. At best it may work for some of you some of the time. Consider yourself warned about the enthusiasm thing.
This phenomenon--that it takes less much less will-power to carry out a predefined plan than to continually make decisions while acting--is well-known to athletes, especially runners. I think most people who train would agree that the hardest part of a workout is getting started, and it takes surprisingly little will-power to finish. There have been some interesting studies showing that an experienced runner maintains a constant pace on a long run--he has an nonconscious sense of the pace he will be able to maintain, which is largely independent of his current motivational state. Training books never say "run as far as you can at this pace"--this would be mentally and physically exhausting. Runners are often urged to set a pace and distance for themselves before starting the run.
From my experience there's also a long-term feedback process that affects how hard it is to start the activity. If I set myself a workout plan that is too strenuous and leaves me exhausted after each workout, then it becomes harder and harder to start, and after a while, I'm not putting my running shoes on.
So if we can generalize these lessons to other activities that normally require will-power, they would be 1.) set a plan (on whatever timescale is sensible) and follow it so you're not exerting will-power constantly, and 2.) set yourself a pace so that if you follow your plan, you don't feel exhausted afterwards--that way it will be possible to sustain the plan in the long term. Regarding (2), people have suggested enforcing a schedule like "45 minutes work, 15 minutes break", though I haven't tried this myself.
I think that by far most-powerful willpower hack of all is making oneself accountable to other people, but that's a topic for another day.