I finished year 11 with 3 Bs and the rest As and A*s in my GCSEs. What worked best for me was exam specifications. Don't underestimate them -- they literally tell you exactly what you need to know. Some of my teachers printed them off and handed them around during revision sessions, but they're pretty easy to find on exam board websites.
Take advantage of after-school or weekend revision sessions. I didn't do this enough. That, and start revising early on! Don't leave everything to exam season because it piles up quicker than you would have thought. Retaining small bits of information over a longer period of time is recommended, especially as you may have more than one exam on any given day, and cramming two subjects' worth the night before, in my experience, is obviously not a good tactic.
Lastly, you obviously have the motivation to get what you want, which is essential in itself. But don't stress. All As will give you more UCAS points and open up all A-level/post-GCSE options, but people do best at what they enjoy. Don't worry if you find you're not equally good at everything, because the aim of GCSEs is to help you to choose what you want to do after school from what you're best at and what you enjoyed the most.
Work hard, do your best, listen to your teachers and you will do great. Good luck and well done. :-)