(This is just for GCSE right?)
Base revision notes off past papers, or just do past papers.
Flashcard app - anki (also a program and a web version.) (Takes time to get to know how to use it.)
If you go about this the right way (unfortunately not so many people know how to do that), you can learn a ridiculous amount of stuff in a short time.
This is apt and perfectly fine for GCSE.
Need any help w/ biology or chemistry, ask TSR (or me for either bio or chem, as I'm doing both for A level. Won't guarantee to know anything, but I'll at least know most.)