Know your texts well. As obvious as it sounds, it's something that people underestimate. Read them a few times, familiarise yourself with the content, any characters, themes etc.
Memorise the assessment objectives. You could write a beautiful essay, but don't hit the assessment objectives effectively and you're in for a shock!
Don't leave revision until the last minute, especially if it's a closed book exam and you have hundreds of quotes to remember!
Get your coursework up to the best possible mark you can, it could save your life draft it as many times as you're allowed and keep up to date with it!
Practise essays when you can. This is something I wish I had done because it's extremely beneficial in getting the perfect structure embedded into your head and ensuring you can write a decent essay within the time limit
What exam board will you be with? Do you know what texts you will be studying?