I did my gcses about 5 years ago but gcses are literally a memory test unlike a levels.When I revised for them I made a revision timetable (prioritising the subjects I struggled with), would use colours, highlighters etc. I used cue cards as well and would gradually reduce the amount of info I put on them. Use sticky notes as well- stick them on your wall etc because as you walk past them you'll start to remember the info. Get people to test you. And most importantly, do past papers!!!