If you haven't yet put the manuscript away for a rest, do so after four or five rewrites. Your eye and inner ear will need the break, and you will be more ruthless when you return to it. When everything is fixed as much as you can fix it, look again at the first five or ten pages of the first chapter, especially the first five paragraphs. Your opening scene is your only chance of capturing a reader, so it has to be right. And then you're done.
Some people do three or four, others do a dozen.
Always do one more than you think you can bear to do. Then send it out. Caro Clarke Articles 1. Beginners' Four Faults 4. Too Much 6.