Essay editing guidelines: common grammar mistakes
Essays are in the editing. There are a lot of structural thing and revisions to the content of your essay, and this is the sort of thing that should be done first. Ideas are more important that grammar. However, grammar is still important. However, realize that if you are editing a paper for grammar, make sure that you have the ideas and content down first, because if you edit your grammar every time as much as possible you will have to do this at every revision. Far more efficient to sit down and do it all at once. Grammar is important to edit, because an essay with poor grammar, no matter the ideas, will be looked down upon.
As for common mistakes, a big one is going to be sentence structure. The big things that you should look out for here are comma splices and run out sentences, things of that sort. These are fixable, but they are stylistic problems and will decrease the readability of your paper. This is a strange thing because it sits halfway between content and grammar editing, and therefore you should work on it first. When you have a paragraph, you should make sure that your sentences are all of various lengths. This smoothes the paragraph and makes it readable.
The next thing that you should concern yourself with is very common uses of homophones and the use of the wrong word. A good example is that many students confuse words such as theirs, there, and they are. There are other similar words and other situations where people often choose the wrong word. These are simple grammar issues, but they look very amateurish when not fixed. The other sticking point is the difference between it and it's. It has is a very weird case because it means it is, whereas "its" refers to possession, which normally has an apostrophe. Make sure you remember this distinction.
There are also certain formatting conventions that you should follow, but they vary a lot. The big thing to keep in mind is that you should use consistent formatting throughout your paper. This means thinks like choosing between 5 and five, or how decimals work, or the way dates are formatting. This is in the details and not something anyone is really going to call you on, unless you are using a specific formatting style or have specific instructions, just be sure that you do not change it around. Inconsistency will be noticed, to the detriment of your work.