Agreed with Mesopotamian's advice, those are both really good resources that I would recommend above Mathsgenie for A-level content. If your school uses Integral, you can also check out their resources.
My general advice for A-level maths in terms of what you can do to help in lesson is to take notes on what the teacher says as well as what they write. So for example, if your teacher writes a long solution to a problem on the board, they probably just write the algebra, but verbally explain why they do each step. You might understand in the moment, but when you look back at the copied example later, you don't get it. What can be handy is to write down any reasoning your teacher gave for each step - and if you don't know how your teacher knew how or why to do a certain thing, ask! Then you can note that down. I find this made my A-level notes really useful to refer back to when I was stuck.