Before seasoning the fish, make sure the skin is very dry. Damp skin will not crisp.
Before putting oil in the pan, make sure the pan is very hot. If the pan is still cool when the oil goes in, the pan is more likely to be sticky.
Before putting the fish in the oil, make sure the oil is very hot -- at least 350F for anything but olive oil. Oil that's not enough will steam the skin rather than crisp it.
When you put the fish in the pan, don't move the fish to try and keep it from sticking. After a minute (at least) shake the pan gently to see if the fish moves. If it does, use a fish spatula to gently turn the fish. If the fish won't move with gentle shaking, give it another 30 seconds before shaking. Check by shaking every thirty seconds until 3 minutes total have elapsed.
Then, if the fish will not move as a result of gently shaking the pan try and push it with the side of your spatula to get it moving. If you cannot push it free, only then (carefully) slide the spatula under the fish.
Be careful when you turn the fish. Use your fingertips to steady the fish on the spatula. When turning something as delicate as fish, two hands are much better than one.
Turn the fish and cook the second side roughly 20 to 45 seconds shorter than the first.
Keep track of the time. Fish which falls apart is generally overcooked. If you're overcooking, cook your next batch at the same heat, but for less time.
Crisp fish skin is not particularly easy. There's a learning curve to this. So be patient with yourself and keep at it.
Hope this helps,