I've always thought of this in terms of "improving the first derivative", or working not only on current knowledge but on the rate at which we are acquiring knowledge. Improved tools are a great way to increase the rate of change. Some other techniques are improving understanding of foundational topics (dependencies), inventing better representations of the problem domain (e.g., notation in mathematics and computer science), improving one's health (so as to operate at peak efficiency) through things like good diet and exercise (there are many cognitive benefits of exercise), and to the extent that fluid intelligence may be malleable, working to improve intelligence itself (e.g., dual n-back as in the 2008 Jaeggi et al. study).
We use heuristics when we don't have the time to think more, which is almost all the time. So why don't we compile a big list of good quality heuristics that we can trust? (Insert eloquent analogy with mathematical theorems and proofs.) Here are some heuristics to kick things off:
Make important decisions in a quiet, featureless room. [1]
Apply deodorant before going to bed rather than any other time. [1]
Avoid counterfactuals and thought experiments in when talking to other people. [Because they don't happen in real life. Not in mine at least (anecdotal evidence). For example with the trolley, I would not push the fat man because I'd be frozen in horror. But what if you wouldn't be? But I would! And all too often the teller of a counterfactual abuses it by crafting it so that the other person has to give either an inconsistent or unsavory answer. (This proof is a stub. You can improve it by commenting.)]
If presented with a Monty Hall problem, switch. [1]
Sign up for cryonics. [There are so many. Which ones to link? Wait, didn't Eliezer promise us some cryonics articles here in LW?]
In chit-chat, ask questions and avoid assertions. [How to Win Friends and Influence People by Dale Carnegie]
When in doubt, think what your past and future selves would say. [1, also there was an LW article with the prince with multiple personality disorder chaining himself to his throne that I can't find. Also, I'm not sure if I should include this because it's almost Think More.]
I urge you to comment my heuristics and add your own. One heuristic per comment. Hopefully this takes off and turns into a series if wiki pages. Edit: We should concentrate on heuristics that save time, effort, and thought.