It is difficult to recommend something safe because I do not know your subject and the subject of the essay, and I did not see your current work to read it and find possible errors. Could you be more detailed with the question for the best answers? 🙂
However, in general, I can say from my own experience with writing essays that to improve any kind of work, it is important to avoid some common but serious mistakes.
The most widespread in your case among students are:
– It is not a good understanding of all your homework / subject
– Absence of clear theses and thesis, also a plan for all the work.
– lack of good scientific / informational resources according to their subject
– poor vocabulary, style and grammar.
– errors with formatting
– weak introduction and conclusion
Also the important problem is the lack of revisions and editions for your work ready, you should leave enough time for this and review it carefully at least several times. The new perspective of other people can also be very useful because they can see the errors that are hidden for you. Your parents and friends can help you with this, there are also professionals in writing https://homeworkneeded.com/ that can be useful to improve the trial as well.