The body of your essay needs 3–6 paragraphs, each presenting one idea. Once you know the elements your paragraphs should contain, you'll find it really easy to write them.
Your conclusion needs to sum up your essay and argument in a memorable way. It's the last thing your reader will read, and there are tricks to making sure they remember it.
When you think you've improved your work as much as you can, ask someone whose opinion you trust to read your essay. Most of the time, they will pick up things you've missed.