A lot of people seem to emphasize setting the hook "quickly". I believe this is poor advice. It should be a smooth, firm motion. You don't want to jerk the fly to set the hook.
I think most hook-set issues arise from less than ideal line management. Hook-set technique will necessarily be different depending on tactics... obviously you would use a different motion when using a dry fly compared with czech /tight-line nymphing due to the disparate amounts of slack line. If you have a lot of slack line, you'll want to pull line with your opposite hand as you set the hook to pick it up.