Don't use no double negatives. Make each pronoun agree with their antecedent. Join clauses good, like a conjunction should. About them sentence fragments. When dangling, watch your participles.
Verbs has to agree with their subjects.
Just between you and I, case is important too. Don't write run-on sentences that are too hard to understand because of their length and complexity, just to name two reasons of many that could be named. Don't use commas, which aren't necessary.