Most of the fish you'll catch will be on LIVE bait
(although you can use artificials to catch certain
species).
The first thing you want to do is pick the boat for
the task. I usually go with a craft that has greater
REVERSE speed (this places less tension on the line
and helps you land the fish much quicker). Although
you might try a faster turning boat for fish that
have blazing turn speeds like Mako sharks and certain
billfish, after you're on the water here is where
things get tough.

Leave your drag set at the middle.
When a fish strikes, start reversing the boat and try
to keep the line and angler (guy in boat) in a straight
with each other because it places less stress on the
hook and line as well. As the fish starts to become
tired there will be more white and less red near the
marlin on the fight meter; this is the time to start
reeling.
Click on the mouse button as you chase the fish. The
added tension will wear them down so they do not run
off with your line.
Another thing to remember, especially with marlins and
other fish, is that they're very "boat shy." Expect
them to start hauling fin when they're near the boat.
You also have to watch that the fish doesn't get under
the boat; otherwise it'll snap the line automatically.
Try to keep the boat BEHIND the fish, especially when
near the boat; then you can park the boat over it as
you finish it up.