So get your ideas down, put it away for a few weeks and re-read it. That way you're looking at it with fresh eyes. Try and read it from a readers perspective itms? And not as a writer. Make notes on what you think needs changing and then edit it. You'll be able to slow down where you think it needs slowing down and remove any bits you think are unnecessary.

Stephen King's "On Writing" is a very good book to read for writing tips.