It's strange, I find biology the easiest of my A-Levels (I get A's in it, but I get consistent D's and U's for History).
Like another user said, it'd be good to know what spec you're doing. Either way, I think the main thing you NEED to do is past papers. Trust me, I used to hate past papers. It was an absolute pain printing them all off, and I always thought "these questions came up in the past, so they're never going to come up again. So why am I doing them?" But after a while, I realised that past papers were the KEY to getting a good grade.
Biology is tricky because there's often a lot that you can write in answer to a question, but there are probably only like 2 or 3 things that the exam board will accept. That's why it's so important to do past papers.
I remember during GCSE's, before I started doing past papers, I got C's and D's pretty much every time. Then, I crammed past papers for the last three months or so and came out with an A.
So I'm definitely doing that for A-Levels this year, and I think that you should too.
You still have over six months until the exams. Try and do one past paper a week, two if you can. By the time you get to the exam, you'll have seen everything. And you don't HAVE to print everything off either, just have a pen, something to write on and the markscheme and past paper up on the computer or smth.