While at Pioneer, I taught other students various topics in math competitions every week during senior year. An extensive guide was also written about math competitions and the many other resources available. You can find them here.
You may find it helpful to use the Math Competitions Tracker App, which was my final project for my react native class.
Also during senior year, I held biweekly meetings to cover topics in Competitive Programming, which involved Data Structures and Algorithms and their common uses in competitions. An extensive guide was also written about cs competitions and the many other resources out there. You can find them here.
Similar to the math competitions app, there are websites out there that can track your progress on various competition websites. Two well known ones are CLIST (mine) and kenkoooo (mine).