For the higher mark questions in particular (especially but not only geometry), past paper questions are essential. Many of these questions will be based on concepts that aren't that advanced and can often be found in the formula sheet provided (trigonometry is the big one), so the real challenge is figuring out how you should approach the question. Knowing the cosine rule is great, but ultimately useless in these questions if you never think to use it.
Practice paper questions can really help with getting more familiar with these tricky questions, and are, in my opinion, a necessary part of revision.