Look at the next jump before taking off a keep your eyes on it till your about to take off for that jump, and look to the next.
Pick a spot right in front of you and look there. When you go over the jump pick your head up and look at it! Hope I helped!
Don't hollow your back out over the jump and spot something and keep looking at it over the jump
Try to look over the jump and maybe go back to the basics and practice small jumps because they are easier if you are on a higher level and you can think about your position a little more. I have a habit of putting my shoulders forward and not really sitting back so my trainer always exaggerates and says lean back a lot like you're going to lay down on the horse. When I do this, then I am in the right position. So try to "sit up and look forward" and exaggerate this and this will probably help.
I hope this made sense (LOL) and helped you out!
You could practise some more complicated courses where you have to be constantly looking up to your next jump. Or have someone standing on the ground reminding you to look at them. :)
To look up, and when you are going to a jump look at something and don't stop looking at it until you're on the ground