Well the good thing is that you already have pretty good grades, and you just need to work on improving the AS ones a bit. I think it is entirely possible, when we motivate ourselves its surprising how much we can achieve.
For study tips, I recommend taking one spare day a week, or an hour at the end of each weekday and writing a essay plan and some revision flashcards of each module and its highlights that you learnt that week (this helped me immensely in my first year at Uni), go over them all every so often, take a blank page and do a spider diagram of the module also and its main points to remember. And it will make sure your revision is already prepared for exam time, its all about doing things in good measure.
Unfortunately I studied History Sociology and Law so I can't help with the actual modules, just know that your teachers will teach everything needed to pass the exams pay attention in class. The fact that you are finished with the EPQ and dropping maths will ensure you have more time for the other three A levels, so that is really useful, you can definitely get three A's if you really want to, and your GCSE grades were amazing, good luck.