When I'm spraying, usually with a can, I spray very light coats from a fair distance, say about a foot or fourteen inches, and try to spray each area just once. Ten just build it up using several coats. This way I usually avoid runs, but if they do happen, it sometimes helps to blow hard on it to try push it to the edge or just until it spreads a little. The thing to remember about having the paint or the workpiece warm is that it will make the paint even more runny. Mark is right about specks of dirt, which can be pretty annoying, but I usually only get them when brush painting. Another good tip is to get a shaving brush, you know the type for putting on shaving foam, and use it to clean the models. It works better than anything else I've ever tried