Overthinking issues that are really very simple
Counter-signallign as a smart-person mistake
Valuing intelligence above all other qualities
Rigidly adhering to rules -- compare the two endings of "Three Worlds Collide" and the decision by which they diverge.
Expecting other people to always be rational
Got nothing for the last two. I don't think the last one is a mistake that very many people at all make. (I think being right about things has surprising benefits well past the point that most people can see it having benefits).
Other smart person mistake covering posts that spring to mind: http://lesswrong.com/lw/dxr/epiphany_addiction/ http://lesswrong.com/lw/j8/the_crackpot_offer/
And a lot of the general mistakes that LessWrong warns against are just person mistakes, rather than smart person or normal person mistakes. [edit: grammar]
Adding to this:
Directly pointing out people's flaws
I also don't see the problem with valuing being right highly. I can see the problem with letting people know that you are right too much.
While LessWrong contains a large amount of high-quality material, most of the rationality advice isn't actually targeted at our core audience. The focus seems to be more on irrational things that people do, rather than irrational things that smart people do. (Sidenote: If we wanted to create a site focused on spreading general rationality, then we'd need to simplify the discussion, remove a lot of the maths/controversial ideas and add in some friendly images. Does such a site exist?).
This has led to a number of comments questioning the real world value of having read the sequences. If your average person had the patience to read through the core sequences and understand them, they'd find them extremely valuable. It'd provide them with a glimpse into a new way of thinking and even though they would likely hardly appear to be very logical to most Less Wrongers, they'd be much better than they were at the start.
On the other hand, most Less Wrongers already know the basics of logic. That's not to say that we don't act extremely irrational much of the time, but just that going over the basics of logic again probably provides minimal benefit. What is needed is something specifically targeted at the kind of irrational mistakes and beliefs that intelligent people make. I would argue that if this were a sequence, it would be the most important sequence in the entire site. But, since I lack that level of writing ability, I'm not even going to attempt such a project. So I just created a post where we can list articles or ideas that should be part of such a sequence in the hope that someone else might pick it up
Here are some examples of mistakes that intelligent people make:
Taking a fixed instead of a growth mindset - shying away from challenges, convincing oneself that we are just naturally bad at non-intellectual things and that we shouldn't focus on them
Directly pointing out people's flaws
Overthinking issues that are really very simple
Counter-signalling by ignoring the value of fashion, money, being liked
Valuing intelligence above all other qualities
Rigidly adhering to rules
Expecting other people to always be rational
Not considering popularity as a signal that is worthwhile understanding
Overvaluing being right
I'm sure there are plenty more. Any other suggestions or relevant articles?