One thing I know is when you are missing a lot of bites and they are just nibbles or really light. You can always try using a smaller hook and bait. Usually when they are just barely biting this works to increase your percentage. The down side to this is if your casting it means less weight and less distance. Plus, it increases your likelyhood of getting smaller fish. As far as setting the hook I struggle with the same thing. I usually try to set it hard to secure the hook in the fish, but I still miss a lot that way too. The best time to set the hook is with little slack right at the first sign of a run.