The problems of essays are the confusion of thoughts and their incorrect presentation. And you can write an essay correctly only when you have a clear idea of what you are going to talk about. Moreover, you should keep in mind the most frequent mistakes of novice writers:

1. Sticking to the main topic of the advancedwriters review. When answering a question - talk only about this topic; when talking about yourself - do not go into reflections about eternal things, etc;

2. Clearness of phrases and thoughts, exclusion of complex and vague sentences and turns. 

3. Compulsory proofreading. You are writing for people and, most likely, for specific people. Read the text several times, thinking about whether you will be understood correctly;

4. Do not use scientific terminology in your arguments; write in your own language as you understand it;

5. Do not understand the previous paragraph so that your opinion in the argument seems unreasonable;

6. Fill the text with your emotions.

Difficulties in writing an essay can arise only in one case: if you do not know what to write about. Research and understand the topic (question, object).

Related Resources:

What is an essay? 

How to write an essay? 

Essay outline (structure) 

What is a TOEFL essay