How do you get a lovely, clean edge when you're painting? Well, good preparation is key (it's very difficult to paint a clean edge on a bumpy surface!). A steady hand helps. I don't have a particularly steady hand - but with concentration and technique I can get an edge which makes most of my customers ask how I did it! But one thing that really helps is to overlap your paints; for example, if you're painting a ceiling and walls - first do all your filling of cracks and dents, then paint your ceiling but overlap the paint slightly onto the wall. Make sure that you brush out the paint reasonably flat. Then you can paint the wall colour up to the edge of the ceiling and there will be no gap in the paint. I always recommend doing two coats of any colour - you get a much better finish. I really should do a YouTube tutorial about this one day - as it's easier to show than to describe! If this is too confusing, please let me know.