While I'm not a purist and I do nymph, I have to admit liking dry fly fishing more, being better at it, and doing it when I feel I have even a reasonable probability of success.
Floatant, generally to the whole fly. I usually use a paste, but been using the powdered stuff (Frog's fanny) more and more. The powdered stuff is especially useful for non-hackled dries. Just put the fly in the little jar, cover the opening with your finger, and shake. Pull the fly out, and blow it off. It's great stuff, my biggest problem is that the cast always works its way off in my pack, and now I have a pasty powder covering everything in my pack....
As far as refusals, we all get em and we always will. The fly and the presentation are the two parts. As far as fly, shape and color are somewhat important, but not nearly as important as size and float characteristics. By that I mean do they want it ON the water(full hackled dry), flush with the surface (spinner or comparadun), or just under the surface (emerger). Size is self-explanatory, get those right and you'll do better. Details like color, shape, number of tails, etc., can help on occasion but isn't nearly as important.
Presentation. Most of the time, they want a perfect drag free drift, starting at some proper distance in front of them till the take. It may look drag free to us, but micro-drag plays a role and you're whole day is in finding ways to minimize it. I don't think you ever really fix this problem. I've worked on it and worked on it, and the final score does get better as you get better. But I get just as many if not more refusals than before. Some of the ones that used to refuse now take, and some of the ones that used to ignore now refuse....
There are situations where they actually want it the other way, they're keyed on movement, a lot of egg-laying caddis situations are like this. At these times a really high floating fly, often referred to as a "skipping" fly, can be deadly when drug across the surface. But work on the drag free drift first, and then think about these situations.