I was talking to a friend a few days ago and we were discussing lighting and flash and technique. He mentioned that he had given up on the Nikon Creative Lighting System (CLS) because when he tried it at a wedding it never seemed to work. Then he said that he had gone to using the manual flash settings because he knew that about "that far away" gave him just what he needed.
What he was doing was using his experience, gained over time, to know that at a specific distance, a specific power setting would give him a predictable result. How did he know that? By doing it over and over again until he could remember and repeat it. Now he is on automatic.
You can do that with the CLS system, too. You just need to practice. Do it at home. As I mentioned yesterday, do it on your time, at your home, with your kid, cat, or spouse. But do it. With digital, it costs nothing. You gain the experience that you can take to the next wedding or portrait assignment.
And it works with other things besides the CLS system. Work on using your on-camera light to bounce off surfaces. Try it at home and get a feel for it so when you are on a job you can go to it with confidence.
All these techniques are like tools in your tool box. You could use a hammer (on-camera blast flash) on everything and get the job done. Or you could pull out a screwdriver (bouncing flash to one side) and fix a situation. Or grab a power saw (off-camera TTL-CLS outside) for a different scenario. Arm yourself with the tools of the trade and the tricks of the trade will come.