I want to improve my exposition and writing skills, but whenever I think "what do I know that I can explain to people that isn't explained well elsewhere?" not much comes to mind.
That seems like the wrong question to start with for casual writing. Some version of it might make sense for academic publishing.
Is there some math you're having fun with that you'd like to try explaining?
If you'd like a great big project, how about rationality for people of average intelligence?
Why do you think that is a wrong question? I am mostly asking because I want something interesting to write about, that I would be motivated to write.
The math that I am having fun with I don't know thoroughly enough to explain (and I am learning it from a really good piece of exposition).
The rationality one looks like fun, I will see if I can do some of it. First step, hack it into pieces so I am not working on a massive supergoal project, but a small project instead.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.