Sometimes, we wonder whether we could improve these parameters, and, if so, by how much. I can't emphasize this enough. As preparation for working in finance, Eric mentions a number of courses. Proof-oriented courses are very important. Courses in statistics, calculus, linear algebra are useful for their subject matter.
Programming is very helpful.
You might also be able to get that from crossword puzzles and games magazines, but mathematics was the key for me, as it is for many other young people.