For being self taught you're pretty good!
But I noticed with your backflips its less of a "tuck" and more flat if that makes sense.

You see in your first backflip, you have your arms flat against your sides, and your knees aren't bent, slowing the rotation and making it look a bit stiff and unrealistic:


On your second backflip its a bit better, where your knees are bent, but you still have your arms flat against your sides:


You see with my backflips, I have my knees bent and my arms tucked in and "holding" my knees. This gives a more realistic look, and also speeds up the flip:


Also, on your second flip, you jump FORWARD instead of rotating BACKWARDS, this is mainly because you extended your hips to early. Theres no easy way to tell when you should extend your hips on your launch, its mainly just playing around with it until you get it to work. If you extend to early, you go forward... But If you go to late, your flip gets really low.