The basic observation is that, if we think of life as an optimization problem, then redefining the search space is much more important than making local optimizations; as a fact of human psychology it's hard to consciously focus on both; but we can implicitly get away with doing both by creating mental triggers for when local optimizations are likely to be particularly effective to think about, and by structuring things so that many local optimizations get made automatically.
If you have been to one of the Rationality Minicamps or certain other CFAR events, you may have had the privilege to attend one of Anna Salamon's excellent classes on microeconomics (despite the title of the post, I am being sincere here; you really should attend them if you haven't already). There is too much content to briefly summarize, but essentially "microeconomics" in this context means applying basic microeconomic concepts like marginal value, value of information, etc. to everyday life. For example, if you spend 30 seconds brushing your teeth each day, then spending five minutes to think of something else to do at the same time (like stretching) will save you 3 hours a year, which is a great investment! (There are some caveats to this calculation, but I'm glossing over them as they aren't relevant to the post.)
And indeed, spending 5 minutes (once) to save 3 hours (every year) is almost tautologically a good investment. Now that I've brought up this example, and assuming you value your time, you should probably actually go through this exercise (or just use the stretching suggestion).
I intend to argue against something similar to this but subtly different. Basically, while any given trade such as the one above is good, I think it is a mistake to systematically search for such trades. Note that I also don't want to argue that you should never search for such trades. If you're about to buy a car you should almost certainly put a lot of microeconomic optimization into it, and if you can find things that improve your overall work efficiency substantially, then you are winning big-time. But I worry that, sometimes, the wrong lesson is drawn from these microeconomics examples (or cognitive bias examples, or any other rationality skill), namely that X is suboptimal by default and we should go out looking for places to optimize X.
The reason I think this is wrong is because it aims much too low --- if you really want to save the world, then your average thought needs to be good enough to save two human lives [source: the average human lives only 3 billion seconds]. Even if each individual optimization you make ends up adding to the amount of time you have, the overall process of concentrating your attention on such optimizations makes you less likely to think other thoughts that would be far more valuable. Perhaps another way of putting this is that, even if each small optimization helps you a little bit, the time it takes to think up such optimizations actually makes you lose out --- however, I don't think this is actually it, I think it has more to do with forming mental habits, where you want to form the mental habit of making huge optimizations rather than small optimizations.
What I think people should be more concerned with than micro is what I'll refer to as macro --- the overall structure of the search space (in this case the structure of your life and how you think) --- as opposed to making local optimizations within a fixed structure. For instance, becoming an atheist; or realizing that social skills are both trainable and highly instrumentally useful; or learning to visualize the steps towards a goal; or learning to code; or finding a group of allies that you didn't previously realize existed; these are all examples of what I'd call "macro" optimizations that are the sorts of things we should be looking for. (I should note that a lot of "macro" skills were also covered in Anna's microeconomics units.)
I also continue to think that there is a clear place for micro-level skills, as well. The key is to incorporate them into your thought process, both at the level of creating triggers to explicitly call micro-level optimization routines when they are likely to be helpful, and at the level of restructuring your thought process to automatically be more likely to make good decisions by default. For instance, the lesson I drew from Eliezer's posts on cognitive biases were not that we should go learn about all the different cognitive biases, but that we should develop habits of thought that will automatically notice and decrease the effects of such biases. Then, for a couple of the more pernicious ones like trivial inconveniences, I further added specific alarm bells in my head to watch out for those, but only because I noticed that avoiding trivial inconveniences was routinely harming me.
I'm not sure how good of a job I've done of explaining what I wanted to (it's still not entirely clear in my own head), so I invite your thoughts and feedback. I'd be particularly grateful if someone wiser than me (I'm looking at you, Critch / Wei / Yvain) could figure out what this post was trying to say and then write that instead!