Do more than the bare minimum that is required. Try to read supplementary material.
It is easy with the internet these days (just be careful that you are on a reputable site) to find text and videos to explain almost any topic!
Make out a study schedule for one week, allowing yourself breaks to reward yourself.
At the end of the first week, make an honest assessment of how well you did.
Revise it (in necessary) – and then try to stick to it for the rest of the school year (or term/semester)