well -I try to do at least 1hr after school monday to thursday (I have Friday's off cos well...it's friday lol), if not just fit 15/30mins in wherever u can. I try to do a little more on the weekend, maybe 30 mins on a saturday and 2hrs on a Sunday, but obviously whatever works for you is fine. Even very small revision bursts through the day - like 5 mins trying a question you get stuck on/or forget how to do.
Asking others to help can be really beneficial too, revising with others can be really useful if you try the same question and then compare how you work it out -
or if you prefer to work alone - maybe listen to some classical music/instrumental pop music whilst youre doing it, this can help focus your mind. (try not to listen to songs with lyrics/songs that you know as this can be distracting)