What should I do before writing an essay?

First of all,this is not the first time i write essay.What should I do before writing an essay?
Including:
a.Vocabulary-what vocab should I choose and when should I apply in the essay?I read quite a lot and learnt a lot of vocab but the problem was i can't apply those vocab into my essay.

b.Facts and explaination-maybe this is not so important for me since i could figure it out at preliminary before writing.Just need some guidelines how to divide my facts,explaination.

c.Essay content-How to start intro,body and conclusion also how to divide the paragraph properly.

I couldn't write a better essay not even a good one.I really need helps!!

Glad if you could help.I'm not planing to write story essay instead,im going to write essay about fact or most likely an article.(words between 370-450)

well, it is too difficult to put all your thoughts together in only a 400 word essay, but it is not impossible.

First, the introduction: in 50 words, talk about 'What is the essay about? How is it structured?'.
Then the main body: in 25 - 300 words, write about data review, findings and evidences supporting those findings.
At last, the conclusion: in 50 - 100 words, summarize focusing on the originality of your talk and findings.

be explicit,
be relevant,
be logical,
be clear,
be concise,
support your findings with evidences,
and do not forget the references.

Goodluck