You're flipping because when you jump for the aerial you're pulling back whilst trying to jump. As you probably know holding the direction stick and pressing jump twice will cause you to flip. When going for an aerial you need to jump, let go of the direction stick and then jump again. If you don't release the direction stick you'll just do a regular flip in the direction you're holding. All you do next is boost where you want to go. You can also hold boost while doing the double jumps which will make you even faster. (If you're talking about single jump aerials then you're just pulling the direction stick too much).

As for predicting an aerial you just need practice. You can go into training and just practice flying.