Tutor people in things. (You have to be smart to teach other people things.)
Definitely this. Tutoring is a very strong signal of intelligence, but is really a matter of learned technique. I was able to tutor effectively in Statistics before I had taken any classes or fully understood the material by using tutoring techniques I had learned by teaching other subjects (notably Physics). The most common question I found myself asking was "what rule do we apply in situations like this," a question you do not actually need to know the subject material to ask.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)