After a lifetime of teaching English, I have found that “agreement” is the most perplexing part of learning any language – agreement of number, for example, between subject and predicate (“The people are/is shouting”) especially with irregular verbs or collective nouns, and agreement of gender in pronouns (Maria held her/his hand”), etc. I think this is because students think that knowing the “vocabulary meaning” of a word is enough. (This is a problem in all languages. For example, in French, “le critique” and “la critique” seem to mean the same thing, but they do not.) Following close behind are homonyms and syntax errors; homonyms such as “its” and “it’s” are particularly perplexing.
The most common English students make when in comes to writing essays for English is not allowing themselves enough time to write an essay. A student will sit down the day/night before it is due and write a whole essay out without ever doing any research, free writing, and/or brainstorming etc, prior to starting to write. They then will write a one copy report which is pretty much just hoping for the best.
Even a student that has a hard time writing a paper can write a successful paper IF and ONLY IF they give themselves enough time to do all the work before even starting to write. They need to have their ideas worked out on paper and know exactly what they are writing about and the entire contents of the essay. If they do the work before then you have a much better chance of writing a good paper.
Also giving yourself more time than just the night before it is due has another major advantage, they will be able to write more than one copy, meaning it will be written the first time as a rough-draft and then it can be edited by whomever...teachers especially if they will help! Also it is so helpful to write a paper, edit it and then put it down for an entire week..DON'T even look at it again for an entire week. When you go back to it you have a much better chance of making the paper even a success!