The idea is to make the horse WANT to jump, rather than forcing them over with a crop and a kick. This will simply make the horse more resistant and mistrusting of you, and they'll only jump as they know if they don't then they'll get hurt.
Start off on the ground, lunging them away from the jump and only allowing them to rest near the jump. This way, the horse will associate the jump with rest and will want to be closer to the jump.
Allow your horse to go over the jump after making them work away from it. Once they've gone over, allow them to rest and giving them a treat for going over really helps to motivate them.
This way, your horse will want to go over the jump, as they will associate it with rest and a treat as a reward. My youngster really enjoys her jumping as a result of this way of training her.