1. Answer the question
Obvious you'd think, but often students stray. There should be lots of clues in the title as to what you're supposed to be writing about. Look for Directive Words eg examine, analyse, discuss, compare, evaluate and Key Words - if it mentions the C16th, then don't waste time on the C18th. If you only answer half the question, you can only pick up half the marks.
2. Balance the essay
Essay questions often contain several parts eg with reference to two or three examples, or something along the lines of: Discuss the effects of....Explain why this may be. Each part of the question should get roughly the same space. If the question is eg Discuss the roles of women in C15th France, then work out how many roles women had (religious, domestic...) and take it from there.
3. Work out a structure
If you're comparing two texts you have a choice. Either look at text A for the first half, then text B for the second - AAAABBBB Or look at each text for the same topic ABABABAB.
4. Do some maths
If your essay is to be 2000 words long, each part should get roughly the same length of page time eg deduct 300 words for the Introduction and Conclusion, and a two-part/example essay will spend approx 850 words on each part.
It's a good idea to work out how long you can spend on each part as it can save time by preventing you from doing unnecessary research and reading. If it's the Discuss the roles of women in C15th France in 1000 words, and you've come up with 5 roles, then you know you can't spend more than 200 words on each role. That's not much, so it's a waste of time reading extensively round each role and finding lots of examples - you've only got space for one or two.
Once you've sorted out what you're doing and how you're going to do it, writing the essay is much, much easier - and I'll look at that tomorrow.