Timing
Timing is crucial to catching your fish. Once you see a fish going for your lure, press and hold the "A" button on the Wii Remote and flick it up to hook the fish's mouth. Do this too soon and the fish will swim away. Do this too late and the fish will have gotten the bait and swam away. To get good at timing the flick of the Wii Remote, practice hooking a fish often.
Bonuses
Once in a while, you will see icons that prompt you to do certain things with your controllers. Follow the sequence accurately and you will receive bonus points along with a power boost that helps to reel in your fish more quickly. If you see the icons pop up, be quick about acting on them. Follow them exactly as shown and you will receive the bonus. Practice moving your fingers from button to button as well as moving the Wii Remote and Nunchuk in various directions and you will get quicker when you see the prompt.
Line Tension
Once you have hooked the fish, reeling the fish in requires proper line tension. Too little tension and the fish is liable to escape. Too much tension and the line might break. You use the Nunchuk to reel forwards and backwards until you get it into your boat. Reeling to quickly backwards may create too much line tension and reeling too quickly forwards gives too much freedom to the fish. The fish will always try to escape and will pull back from time to time. You have to keep the line tension steady throughout these changes. Pay attention to the fish movements and your line tension and you will get good at reeling in the fish.