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.