You must be merciless. Especially with a project that you love. Keep in mind: as the writer, nobody else is ever going to love this project as much as you do. Give your manuscript-baby some space, and focus on other things for a few weeks: working on your pitch, putting together lists of potential agents, reading comps (i.e. books that would sit next to yours at the bookstore). After a minimum of one week, but better yet a month or two, you're ready to read.