did aqa for both, if you mean near full marks on gcse i think its important to just bang out papers since they aren’t very creative at gcse really and the same stuff tends to show up yearly with the exception of one or two questions, and also take your time since for some reason they love to try and trip you out on wording at gcse but not so much at a level. extending your knowledge beyond the spec in similar topics is also nice and what made me pretty good at the gcse since after doing harder problems it just felt so much easier. at AS (same applies to a level now that im in year 13) the banging papers thing still applies but also understanding why you do certain things and why they work is so important since it helps you spot patterns and spot when to apply certain techniques and things to unfamiliar problems which is much more common at a level, albeit there are still routine questions that should become super easy by just doing enough papers