How can I write a good essay in exam conditions?

First off- practice as much as possible! The more practice tests you do in exam conditions, the more you'll get used to writing under extreme time pressure.

Make sure you set aside a bit of time (5-10 minutes) in your exam to plan your essay - there's nothing worse than reading an essay full of good ideas, but is poorly organised. Make sure that you know how you're going to structure your essay BEFORE you start writing.

Only include points that you can fully explain. Try to avoid feature spotting and make sure you use your Point, Evidence, Explain!

Don't worry too much about quotes! You can paraphrase a quote if you can't remember it exactly. And remember not to include really long quotes, just a few words long at the most- make sure you don't just drop in quotes without explaining them. P.E.E is important here too.