There are two things you can do to increase the chance of catching a fish:
1. Make sure that you are using the correct lure for the fish you want to catch. (Don't use a fire lure for an ice fish, or a myth lure for a life fish.)
2. Make sure you are using the correct lure rank for the fish you want to catch. A rank 2 lure will have a better chance at catching a rank 2 fish, while the same goes for other ranks.
Lesser _____ Lure: Rank 1 Minor _____ Lure: Rank 2 Common ____ Lure: Rank 3
A few useful fishing spells to aid in your fishing adventures are: Reveal Fish School-Lucky Hookline, WC Commons Winnow ____ Fish-Timor Flamecaster, DS Labyrinth (This makes all the fish except the school specified by the spell flee) Summon Fish, Fish Lullaby, Charm Fish-Frodo Silverscale, GZ Northguard (These, in order, will reset all the fish in the area, freeze all fish in the area, and draw all the fish in the area to you.) Banish Sentinels 1-Yuri Smokesnare, DS Athenium (Rewarded after you finish the quest "Catch 'Em If You Can", this will banish all Rank 1 sentinel fish from the area.)
With Sentinels your timing has to be quick! Try to gauge the speed at which the fish is moving toward the lure. Click 'x' (or spacebar or mouse) just exactly when the fish locks onto your bobber.