1. Characters. Do you have more than one character serving the same purpose or are too similiar? If so, can you cut them or combine them? If you have a minor character that isn't adding anything to the storyline, could you use them in another piece of work? Does your lead character have to many characters helping them?
2. Do the same thing with the subplots. Does the subplot add to your novel or distract the reader?
3. Look at the scenes individually. Are they dull? Are they too long? Is there too much dialogue or description?
Be ruthless. Remember the aim is to get a leaner and meaner final draft!