Like I said earlier, don't fear the jumps, don't fear how your horse will react. My trainer always says "Ride Fast, Think Slow." slow down your thoughts and plan through what you are about to do and the different ways to go about it so you are ready if something happens. Keep your leg on and make sure your pony or horse knows what you want them to do. Center of balance over your ponies, give them their head when you jump, or release, and make sure you tell them they have done a good job when they get over it. You will find jumping is hard but addicting :) don't give up!
Get a trainer. It's a dangerous sport, even small jumps can be very dangerous if you do not know how to ride them, it's a totally different feeling from riding on the flat and it is way too easy to seriously injure yourself AND your horse. I don't know about you, but I can live with hurting myself, but I would feel incredibly guilty if I hurt my horse doing something foolish.