When it comes to perfecting your manuscript, the best thing to focus on is making each sentence, every word, and each punctuation mark count. You have to be able to step back and see your writing from the reader's perspective. Does this sentence add to the story or does it simply act as filler? Does this word pack the meaning you want it to or is it bland and overused? Does your punctuation help convey your message or does it draw attention to itself? You have to look at your novel or short story objectively and work out what works best for your audience. In this situation, quality is more important than quantity.
When it comes to developing a manuscript, however, it is best to come up with many ideas. Personally, I like to keep a journal beside my bed where I write down every idea that comes into my head. Many never go beyond the brief notation in my notebook, but some develop into larger ideas that can branch off into its own story. The more ideas I have to choose from, the more likely it is that I will stumble upon something worthy of attention. When you are brainstorming, allow one note to let your mind move on to another topic. What is most important is to just keep writing down everything that comes to mind. In this case, quantity is more likely to lead to quality.