Each reference in your paper should have at least once cite in which it is cited alone and dicussed for at least a sentence. Citing alone means not having a citation such as "[1,3,4,6,8]", which is a warning sign to reviewers that the writing is not taking these references seriously enough. A reference is only important enough to include if your paper discusses it alone, and its significance to the paper, for at least one sentence.
Singular third person pronouns in English are problematic because they force the write to assume a group is of one gender or the other. As with many grammatical quandaries, the solution is avoidance or circumvention. Here, this often means using plural third person pronouns instead, resulting in the gender neutral pronoun "they". When switching to "they", make sure the verb conjugation in the sentence becomes plural as well.
Surprisingly often, large phrases, whole sentences or even sentence sequences are repeated unchanged at different places in the same paper. Be careful when you move or copy text that you prevent this from happening.
Several handbooks on writing are on the bookshelf of Lloyd's office, C101. Feel free to use these to improve your writing. These books are:
Two resources suggested by Steven are: