Use the Right Test Line
One of the toughest parts of bait casting for beginners is the actual casting of the line. While thinner line is more effective at catching fish, it's also much tougher to cast and control. Start out with a thicker monofilament line to help you develop your casting skills---a 40- or 50-pound test line works best. Once you get the hang of casting with these lines, move on to thinner lines like the 30- and 20-pound test.
Keep Low Levels of Line on Your Spool
A beginning bait caster is going to have line problems no matter what he does. This can create tangles in the spool nicknamed "bird's nests" because they're so difficult to untangle---many times, fishermen prefer to cut the line and re-spool their pole rather than deal with untangling the line. This can take a bite out of your fishing time. Instead, leave at least one-eighth of an inch of space between the top of the spool and the line put onto it. This will give you line space to move freely without getting tangled. It's also recommended you use a sinker weighing at least 1 ounce. This weight will keep tension on the line and reduce the risk of a ball of line getting stuck in your spool. Veterans prefer to keep their spool as full as possible, but many novice or intermediate bait casters will find it easier dealing with limited line than the hassles of keeping their line straight.
Bait casting reels release much earlier than spinning reels. This means if you try to cast it the same way you cast a spinning reel, your lure will hit the water much faster or----if you're casting side-armed---your cast will go way off course. You'll have to develop a feel of casting to figure out where the best release point it, but if you're used to spinning reels, try to release the line earlier in your cast than is comfortable. Compensating for this change will give your casts more distance.
It's All in the Thumb
This is an old bait casting adage, and it's as simple to understand as it is to say. From the casting of your line to control in the water, most of your fishing technique relies on your thumb. Keep your body relaxed and your thumb soft on the line. It'll help you feel what's happening in the water and, consequently, how you should respond to the action.