I would recommend either finding a trainer to help you out or even having a friend, or someone from the barn with jumping experience, to give you lessons. Honestly it's very difficult to know when you're doing it right without someone on the ground giving you advice. Especially if you don't have any jumping experience to begin with... There are many things that could go wrong if you tried to do this all by yourself and it could result in injury or complete frustration on both you and the horse's part.
But to begin with you need to be practicing a LOT of work without stirrups to strengthen your legs and also practice your two point position. It would be ideal to be at the point where you could ride through all of the gaits in a solid two point and be able to post well without stirrups before beginning to really jump. This will ensure that you have a solid enough two point and strong enough legs to be totally independent as the horse jumps without yanking on his mouth, getting left behind, or laying on his neck.
Good luck, and please take our advice into consideration.
I give myself very good advice, But I very seldom follow it