Throw Long
Try casting your line past the shadow of the fish you can see in the water. That way you can reel your line (and bait) toward the fish to entice it to bite.
Use "C"
While it may be fun to shake the Wii nunchuk to catch fish in the game, this method is also more difficult. Aggressive fish are hard to catch in this fashion. Instead, you can just press the "C" button to reel in your line if you have trouble catching big fish using motion controls.
Hit the Ripples
Try throwing your line onto a ripple caused by moving fish. If you hit the ripple you will be notified with an "Excellent," "Great" or "Good" to indicate your success. This method is particularly helpful in catching elusive pink fish.
Fish Reset
Another good method for catching pink fish is to open the tackle box. Press "A" to open the menu and choose the tackle box. When you press "B" to exit back to the main screen, the fish in your area will reset. Keep doing this until pink fish (or other ones you need for your journal) appear on the screen.
Turn the Fish Yellow
Once you go to Easter Island and catch a Friend Fish, the fish you have yet to catch will turn a bright yellow color. This greatly increases your ability to spot and catch fish to add to your journal. This trick does not work with pink fish, however; they will remain pink.