Your essay must have a lot of good points, it can be a really good point and must be logic and if you can, please, no more cliche points.
Grammar check and wide vocabulary, by reading a lot of books, or even newspaper, this will give you a lot of marks. You can try find the same meaning of the word by Thesaurus. (Note: I heard that if you use difficult words or in Malay we call it 'Frasa menarik', you'll get extra points.) Pay attention to simple grammars too.
Spelling is also important, you dont wanna see your teacher laughing at your essay. Even if you have good points and good elaboration, sometimes bad spellings really ruin the whole essay.
Lastly, practice, you need to practice, you can write 2-3 essays per week and try different kind of topic too, then, you'll be more prepared and feel better. I hope this helps and good luck.