Hello ,

There are few tips which might help you .

1. Eliminate all kinds of distractions - Don't try to fool yourself , concentrate on which subject you feel like I need to score good .
2. Use your strongest sensation to memorise things - each and everyone has their own ways of studying , few write while studying , few also draw maps and use some bright markers to memorise those lines again and again like a revision.
3. Set yourself a deadline -  you can keep some Time goal like I will complete this particular topic in this particular time and then try recollecting the answer/topic which you learned in that particular time , timetable might help too.
4. Work when you feel more alert and active - main thing to study you need to feel fresh and do not divert while studying . I prefer to study in the nights that might help too.
5. Dont stress too much - do not force yourself on a topic which are not able to learn even after a particular time . don't stress too much on the grades too .
6. Motivation is the key - human beings are usually capable of so much more then they can imagine , try motivating yourself , no external motivation is needed for us .  do not wait for the perfect moment , start when you feel like studying.

Hope this tips would be helpful to you , Thank you .

All the best.