Your essays are extremely important. Think what you write. Show a logical progression. Essays are a good opportunity to explain unforeseen events that have occurred in your life, and they can influence a reader towards a positive decision on your application. Do not lie, report facts and circumstances that have affected you, or major accomplishments worth noting.
Universities always check, and lies are hard to keep up with.
You will write many papers during your stay. Ask native speakers to correct and edit every paper you send out. Make it a habit. Also research your papers yourself at the library. It is much easier to defend your point if you have done your own research.