How do you Revise?

I want to start revising for Maths and all the sciences now as they are the only subjects i struggle in but I don't know where to start. Do you have any good websites or do you have any revision techniques. I'm going to get a Tutor to help out, particularly in Chemistry and Maths.

Definitely check out revision guides from your exam board for the sciences, make notes and then summarise the notes into flashcards. For Math I'd do past papers and check which topics you struggle on then practise those problems more