The most useful advice on writing I've ever received comes from Gil Rogin, who told me that he always uses his best thing in his lead, and his second best thing in his last paragraph; and from Dwight Macdonald, who wrote that the best advice he ever received was to put everything on the same subject in the same place. To these dictums I would add the advice to ask yourself repeatedly: what is this about?
I like this quote most in particular, I like what it really means. Writing should not be about just writing about a whole bunch of words on a page and calling it a novel. If you watched the New Moon movie premiere with Stephenie Meyer, her advice was to just write write write. Do not consider a novel just a bunch of words written on a page. A novel needs to have plot, interesting dialogue between the characters, twists in the storyline, and an ending depending on if your book is a series or not.