As your revision journey evolves, you will begin to spot areas of strength and weakness. Get to this early, particularly the latter part. If you are lucky enough that your child excels in one or some areas of your chosen exam, then invest time early in the subjects in which they are less confident. The easiest way to identify your weaker areas by sitting an untimed mock together for every subject/paper that is in the exam. Do this early on, it could be with a tutor but if you have the time and the confidence it could be a very positive step on the road to success to do this together. Remember, it's an exploratory exercise and it's designed to find problems. You and mini-you need to be comfortable with this for the process to work. Bad news is good news, because we've spotted the problem(s) early.
By sitting a paper together you can clearly see the questions types or subjects in which your child has a strong knowledge base, those in which they naturally shine and crucially those in which they need extra help and time. You may want to use a traffic light system of green, amber and red; or you may prefer to simply focus on the question types that are new and scary, or old and scarier! Note your weak spots in a journal or notepad - whatever takes your fancy - and build extra focus on these areas into your revision timetable.