I just finished year 11 and i'm now in year 12, here are my tips; Maintain good sleeping pattern, stay hydrated, don't wear tight close ( makes you stressed), plan your revision, take 10 minute breaks every so often, eat healthy, impliment revision with sport or your favourite activity, ASK YOUR TEACHER FOR HELP, stay behind after school if you're unclear, MAKE NOTES and compare with others, listen to soothing music if you have to, USE GCSEPOD and talk to friends.
GOOD LUCK.
P.S smile and stay happy, it helps alot.