I did it with Edexcel - and got an A (only because I handed in beyond the deadline).
At first it seems incredibly daunting, but it isn't and it's easier than you think. The biggest problem for me was looking at all my sources first, then trying to write it, because I was left confused.
Introduction - Write your introduction now. I found breaking it down into questions and then answer them, then rearranging it to make an introduction help. Why did you choose this subject? Why is it important?
Discussion - Then find your sources, and write as you find each source (you can rearrange or delete later) and make sure you footnote as you write (doing footnotes later is an absolute pain).
Conclusion - Then talk about the sources, pros/cons - is there any bias?
There are some textbooks you can buy to help you - but, I didn't find them helpful.
The main thing I can say is - write now, you can alter and edit as you go along.