I started a great thread that has a lot of good information for beginners, as well as others keeping their horse in shape and keep their conditioning up. Barrel Racing Exercises and Drills.
The biggest advice anyone can get when starting a horse on barrels is to KEEP IT SLOW. It takes months and years to train a good barrel horse. It's not something they just pick up in a few months. You never want to push a horse before s/he is ready, you'll ruin your horse that way. S/he will become sour and hate their job.. Check out my thread and you can start from there, the other good advice I can give you is to start with a trainer or someone who knows what they're doing. If you don't want to have a trainer step in and train or help you train your horse, at least have one you can call and talk to when you have a problem.. A trainer can help you in SO many more ways and you can have that in person experience.