Hopefully you have a trainer. Having one will be more affective for your safety. If you don't, I suggest you watch tons and tons of videos whether they are kids doing small jumps, or George Morris teaching international riders. Keep an open mind, and be willing to unlearn to relearn as you start progressing.
Start as low as possible and come on a light seat position before the fence to avoid any discomfort for you and the horse during the take off so that you can learn to get the feeling of the jump without disturbing your horse :)