Enroll in AoPS. I believe every AMC winner in the last decade is an AoPS alum.

I have an 8th grader who is strong at math. They’ve placed in a couple of contests, and I think they have a real shot at TJ next year. They’d like to continue with the math team in HS, but if TJ works out, it will be fairly competitive. Any suggestions on how to prepare them to do well for things like the AMC10? Is it just about practicing old tests, or are there other things that can be done in tandem with that?