Go to an actual jump, you will get it more on lock when you do on different jumps. But for the knuckle you seem to start with a ninja kick but still pop with both feet. Try to swing the other leg back and jump from the front leg.
Spotting the landing on a frontflip can also be hard at first, but you can see the landing pretty soon if you look to the side, not in between your legs. Last thing is just practice, nothing will be better than finding what works best for you by doing
