The first step is to read and re-read the question. Work out EXACTLY what the question is asking you for, and what the examiner might want. Remember, you get marks for content, accuracy and structure. The marks are shared and so it's important to give weight to each section of the marking criteria, e.g. if you want to make a point but aren't entirely sure how you would express this, think about whether its worth it to make a point if you risk losing accuracy marks because you aren't sure how to conjugate the verbs.
Highlight sections of the question if you need to, it's important to pay attention to the verb in the question, if it is 'Analyser', 'Expliquer', or 'Considerer'. This will give you an indication of what you need to do, often you'll be asked to debate, other times you'll be asked to evaluate a particualr novel or play, or you'll be asked to describe a painting or something you've done at lower levels. Keep the 'task' in mind throughout. It can be helpful to go back to the question each time you make a point and make sure you're sticking to the task in hand.
For each type of question it's important to have a planned approach and structure that you can quickly adapt under exam conditions. Having a clear introduction, main body and conclusion will secure you some marks at least. It helps to keep a stock bank of introduction phrases, argument phrases, subjunctive phrases, opinion phrases and concluding phrases which you can structure the rest of your essay around.