The best thing to do is look at exam papers. Go on the AQA website and look at the January 2012 paper. That's the one I did. I got an A. It was pretty ok. Ask your teachers for like exact keywords you need to write in answers. For example, for synapses, you have to include the words neurotransmitters, electric impulses, chemical diffusion and back in electric impulse and so on. Our teacher went through papers with us and told us how to answer them with model answers.
I have done some quizzes and stuff that you could test yourself on if you click on my name. But also try doing past papers because then you know the layout of the questions also try memorizing some of the mark scheme so you know how to answer a question in your test :) I am doing triple science too :P