Biology and Chemistry are both VERY difficult if you did not take triple award science at GCSE, chemistry is especially difficult as the gap between GCSE and AS is huge! I must admit, I struggled at the beginning of year 12 just bridging the gap and organizing my time.
I work every night, even if I don't have lots of homework (you will always have something to do)
Revise, Revise, Revise, as soon as you cover something, try and go over it and make detailed notes on it so it sticks in your head.
Along with these subjects I took Maths and Psychology. Psychology is good but if you hate long mark questions, you'll hate psychology. I think the highest at AS is 12 marks and at A2 is 24 marks :s
Maths became very useful in Biology as for your EMPA (it's like an ISA that you would've done at GCSE) as you have to use statistic equations such as Standard Deviation, and all the terms that are with statistics eg Qualitative, Quantitative.
However, Maths is a very demanding subject and if I had something else that I wanted to take, I wouldn't have taken it and will be dropping it when I finish my AS.
I hated English so I didn't take it but I know my friends that did take it, enjoy it a lot.
Good luck!