For grammar and spelling excellence, look at comma splices, fragments, and subject-verb agreement.
When it comes to referencing, ensure all references in your paper are in the reference list, alphabetize the reference list, and make sure that all the references in your reference list are in the paper!
For formatting, look at things like, font type, spacing, font size, your table of contents, figures, and tables.
Lastly, when it comes to style (very very important!!), look at run-on sentences, making sure you keep your paragraphs short, reducing each sentence to its essential part. Avoid the overuse of subordinate clauses, and get rid of adverbs and adjectives as often as possible.