The most common mistakes I make are things like expression errors or comma splices.
Well, a comma splice is nothing difficult to understand. It's when you write the way you talk, you might put two sentences together using a comma instead of a period (like this sentence). That is incorrect, but easy to fix:
It's when you write the way you talk. You might put two sentences together using a comma instead of a period
Sex is a motif that frequently occurs (I think "occurs" is best here, because it's not unnecessarily complicated. Frequently reoccurs is a little redundant) in the novel, "The Catcher in the Rye". This motif
seems to play a significant role affecting (try saying something different about how it affects them)----> the surroundings and thoughts of Holden Caulfield.
Keep your verb tense consistent:
When Holden suspects that Stradlater had sex with Jane, it makes...drives him...
:-)