Here are some useful tips:
1. Read the essay topic 2 to 3 times to ensure that you understand it well.
2. Generate ideas and choose the most relevant ideas.
3.Support and extend each idea.Use proper linking words.
4. Make a good mix of simple , compound and complex sentences.
5. Learn the art of paraphrasing. Topic specific vocabulary is important.
6. Make your stand clear in the introduction and repeat it in conclusion.
7.Seek guidance of any experienced trainer to get feedback on your assignments.