If you tend to finish early, you are already in an excellent spot. I think the key is simply to balance doing questions thoroughly and doing them reasonably quickly. You don't want to rush over key words in questions or make silly mistakes because you were trying to finish, say, half an hour early. But you also don't want to be so careful that you struggle to finish.
For me personally, I find that if I rush through and finish with plenty of time left I tend to be lazy when going back over questions. I'd simply assume that I had done something correctly and look over it half heartedly. This is what I found to be true especially in further and methods where I consistently finish exams an hour early and 40-50 mins early respectively. Instead my new strategy has been do nail the questions on the first go by doing at an absolute snail pace. Doing so still allows me to have ~15 minutes left in the end which I believe is sufficient.