My best editing tip is to read your piece backwards, one sentence at a time. It won't help much for flow, but it's invaluable for picking up typos and re-use of words. The theory is that after writing, reading and editing a piece, you know how it goes and your expectations of what's there get in the way what's actually written on the page. It works pretty well for me most of the time, but YMMV of course.