Great questions Travis.
First, I will admit that my experience is limited and this may all be very elementary, but....
1) I have started changing often. In our tailwaters I know that the fish are there, so I have to find them and interest them in what I offer.
2) The first thing that I try to do is find where they are feeding as far as depth is concerned. Sometimes I do this by fishing two or even three flies. Other times I change flies, weighted, emergers, etc, or presentation; stripping across the surface, fishing the swing, high sticking, bouncing a weighted fly along the bottom,etc. (I hate using strike indicators so only use them as a last resort.) I do fish a dry fly with a dropper occasionally. Usually if the fish are feeding on the surface, it is apparent.
3) I do keep a separate box of flies that I plan to fish any given day. Often I tie these the evening before. For some reason, a freshly tied fly for a particular outing catches more fish. I know, this is psycological, but it works.
4) No, I have no quick turn-around time for changing flies. I hope that others post some ideas in regards to this.
5) The one thing that I have learned lately is: "if it ain't working, change something"! I may get skunked this evening, but I can almost always find something that works at least for a few fish.
That's my two cents.
I hope that others with much more expertise than I have will respond.
William
p.s....I agree with Grumpy; depth, presentation and size.