Like cowgirl said, check out the book by Charmayne James. I have it laying around if you want it.
Until then, focus on dry work (No barrels). Your horse should be soft, supple, and responsive. You should be able to move her front and hind independently, move laterally off the leg, shorten and extend strides, stop and back smoothly, have smooth transitions, and be able to lope a consistent circle. Once the horse can do all of this, you can begin working the pattern. There are a bunch of threads about this if you just search "Barrel" or something similar.