Try watching GoPro videos on YouTube of showjumping or cross country
There are many ways to help you with that problem.
First of all, you need to know the amplitude of your horse and find the "right canter". To have a great place, you need to go close from a vertical and a little more away for an oxer.
You can work on small obstacles and count out loud 3 strides before the jump, at the beginning it will be hard but if you repeat it oftenly you will see them coming.
You can help yourself with a ground pole 2 strides before the jump, it will help you "feel" and "see" the strides come because the horse has to fit in the distance.
Then, you can make a ligne of two small obstacles (or even just ground poles to begin) separated from 5strides and count them out loud. Once you succeed doing it, you can try to reduce them (4strides by pushing more the horse or 6strides by holding him more).
Finally, you can ask someone to be with you and tell you when the horse is about to jump to know when to follow him, it can help you. You can also try to jump while closing your eyes to "feel" more the strides and the movement of the jump.
I hope I could help you :)