Here are other tips:

1. If a topic is provided then make it more specific when you start writing. Let your ideas flow but make sure they are unified and coherent with each other.

2. Focus on your main point. Think of your audience or would be readers. (Do you think they will understand what you are trying to say or write?)

3. Once you had expressed your main point, start writing with your examples, details and facts to prove your point.

4. Write a very good conclusion to convince.

5. If you have the luxury of time, review and polish your essay before submission. (spelling, grammars etc.)

Keep in mind that the standards on grammar and such here are very low. Enforce higher standards for yourself.

The more answers you write, and the more varied the subject matter, the more easily essays will come to you when you are presented with a topic.