Move It
Although it is usually best to do everything you can do to avoid moving your dry fly on the water occasionally it works to break the rules a little.
Recently I was casting to cruising fish on a lake and found this to be the very best way to catch them. As the fish cruised, it was difficult to always get the fly right in front of them but if I got it close and then gave it a twitch the big rainbows would see it and come right over and slurp it.
This probably only works when fish are acting reasonably aggressive and probably isn't the best tactic when fishing mayflies or other hatch matching bugs to rising fish, however, if you find yourself throwing hoppers or other terrestrials on stillwater or even on slow moving rivers or streams try giving them an occasional twitch and then hang on.