Getting yourself into position should happen quickly, basically as the horse is changing from his final stride into a jumping position. You will be learning to do this transition so it takes you only a few seconds.
Basically, as soon as you get the feel for how to shift your weight, you can start trying it in the saddle.
Part of lining up the horse properly means you are sitting up and looking straight at the jump, which helps to push the horse in the proper direction. [9] X Research source
During this time, you should keep contact with the reins and the horse’s head, but let the horse balance himself as he will. Also, you can keep one leg in the jumping position as you head to the next gate. [14] X Research source
For instance, you can start with just rails on the ground. Another way to introduce a horse to jumping is trail logs. Because they’re round, there’s less chance the horse will hurt himself. In addition, let him jump in the way he feels like when he first starts jumping. That is, he’s inexperienced and will not be jumping properly yet. In time, he will learn, but in the meantime, still try to get into position as he jumps. In addition, try using a neck strap to help you stay on the horse. [20] X Research source
If a horse decides to have trouble with a particular jump, have someone lower it for you to help the horse build confidence again. [24] X Research source
