I absolutely agree with mmzz about never leaving a topic without fully understanding it. If extra assistance is not forthcoming at school, then take the initiative to use Bitesize, Khan Academy etc.
My advice to parents would be to really get to grips with the specification for each exam. Which board? How many topics are there? How will those topics be examined - essays? short answers? Which paper examines what? Is there any course work and, if so, what are the deadlines for submitting it? If possible, get an idea of which topics will be taught in each term. My DS didn’t really clock when he had finished one Geography topic and moved on to another one, so when it came to revision, there was a lot of sorting of notes + handouts to do.
Finally, don’t give up all extra curricular stuff - music and sport have been a life- saving release mechanism for DS this year.