Writing essays well is not easy, and it depends on what the essay is about. Also, different people have different styles, so I don't know if this will work for you or not. Here is what I did, anyway (I just finished year 12, and we had to write a lot of essays).
Preparation (Very important- do not start writing the essay until you have done this, or something else that works for you)
1. Work out what points you want to make, and write them down somewhere else
2. Decide which points are the most important and which are the least important
3. Get rid of your 3 least important points (or 5 or 2 or whatever depending on how many you have and how long the essay is supposed to be. In any case, drop the least important points)
4. Think of a nice short sentence for each of the points that summarises them, and think of another nice short sentence that summarises the whole essay
Actual essay- Introduction
1. Write down your nice short sentence that summarises the whole essay at the beginning
2. Write down your short sentences for each point, or something similar to them, in the order of most important point to least important point
3. Write down something that links in to your most important point