Here's a quick, everyday one: whenever you come across a sentence that starts with "research says" or "studies show", Google to check whether these studies actually exist, before changing your degree of belief in the claim.
For a more general idea: try changing things.
If you like cooking, try changing your recipes one step at a time to see which ingredients or steps (generally not mentioned in written recipes) actually make a difference. For instance, when making pizza mixing the yeast with the flour makes the dough rise better than pouring the water directly over it, and leaving out the salt makes a huge difference in taste. (Sometimes these experiments happen by accident.)
Change your driving style (from aggressive to smooth or vice-versa) to check for an effect on mpg.
Try deliberately changing your posture in social settings, looking for postural echo. Try smiling more or making more eye contact, see if that changes any outcomes relevant to you. (This seems to count for a fair bit in public speaking.)
Take a different route to work tomorrow, see if your current routine really is optimized for travel time or whatever else you value.
Ask your boss for a raise. Ask someone for something you haven't dared ask for previously. (For instance, ask for a discount the next time you shop anywhere.)
I've read a bunch of times on LessWrong about how important is to test things. It makes sure your beliefs are paying rent and helps you verify your hypotheses. Testing ideas is obviously important to science, and it's about as obvious that testing ideas in everyday life can serve the same purpose. I know all this, and I want to be the type of person that goes out and verifies my beliefs by experiment, but still I can't think of a single time I've done it. I don't think I even recall thinking, about some everyday type of thing, "hmm how could test that?" (apart from trivial trial-error computer related things). Anyway, I was wondering if some of the you could give me some examples of times you've done this. I'm thinking maybe I'll be able to pattern-match the kind of things you guys have done and hopefully recognize in the moment when I'm looking at a testable thought.
Thanks.