Make notes of each chapter. Mind-maps tends to do that well. 

If possible, get past-year papers. Understanding what the question is asking for and learning the question answering technique is critical. 

Seek help outside of school if necessary. Strong foundation at lower sec will position child well for O levels. 

get the guide books, more concise and list the key points. For history, be exposed to more questions to sharpen the PEEL techniques.