A book on of my graduate progs always cited. . . "elements of style." I don't know a lot about it, but it gave good pointers into how to fix common mistakes and proper usage of commonly misused words and phrases. I'm guessing if you go to any good book store there are a host of those type of books. You may also choose to have a favorite prof proofread your papers and ask them to be extra critical and suggest how to improve.