To expand on what fiction said, be aware that your momentum significantly affects your aerial. If you're going fast and try to jump and aerial for a ball that suddenly pops up, there's a good chance you might miss and fly underneath it. Instead slow down, orient your car to where the ball will be when you get there, and then take off. You can also jump and boost at the same time.
If you end up boosting too high, or feel like you're going too vertical, you can push the nose of your car down--either more parallel to the ground to get more forward momentum in the air or angled more downward if you're flying up too high or want to shoot downward. Again, be mindful of your momentum and direction or you're going to waste a lot of boost correcting your course.
