Be natural! Write in plain English, not in 'Essayese'.
Lots of people, when they come to write an essay, start thinking and writing in Essayese rather than in English. Essayese is a mysterious, over-formal, unnatural, and cumbersome foreign language. It is not actually taught in any school or university that I know of, but it is tacitly learned in an as-yet unexplained way during people's teenage years.
Essayese reads rather like a bad translation of a foreign language into English by someone with a grasp of neither the foreign language nor English.
In Essayese, the English phrase 'I think' is replaced by odd phrases such as 'it is arguable to propound the view that', or 'it can be reasonably propagated that', or 'the argument that is being postulated here is that'.
Essayese phrases for the English phrase 'This argument is wrong' include 'This point of view must be seen by us here as being utterly fallacious' and 'We must observe that this flawed position is nonsensical and can obviously not be allowed to be upheld'.
Essayese terms for the perfectly good English words 'says', 'states', or 'argues' include 'expounds', 'propounds', 'decrees', 'affirms', 'proclaims', 'dictates'.
Don't worry about using words like 'wrong' and 'false' or like 'says' and 'argues' too often. They are words that will often need to be used in an academic essay. It is much better to use these same plain English words several times than to use forced and unnatural alternatives just for the sake of variety. I have never decreed, propagated, propounded, or expounded anything in my life; but I have thought, said, and argued many things.
Essayese also contains lots of superfluous adverbs. As a general rule, be sparing in your use of the following:
- 'Probably', 'basically' (these add nothing and make you look unsure of what you are saying).
- 'Clearly', 'obviously', 'inevitably' (the arguments and claims that you will be evaluating in your essay are very unlikely to be 'obviously', 'clearly', or 'inevitably' true or false, convincing or unconvincing — these adverbs are too often used in the place of a good explanation of why a position is right or wrong).
- 'Incredibly', 'amazingly', 'unbelievably' (these are almost always excessive — a simple 'very' or, sometimes, 'extremely' will normally do the trick — don't gush!)
Of course it is true that writing an essay requires a more structured and formal use of language than would be appropriate for e.g. having a chat with a friend. However, as a general guideline, the following is useful: never use in an essay a word or phrase that you would not dream of using in conversation with a friend.
Indeed, one of the best tips is to imagine, when writing your essay, that you are explaining the topic and your argument to a friend who knows very little about the subject. If you have actually talked to a friend about the essay before you write it (see above) then this should be all the more easy to accomplish.