Alright, a major thing that makes you rotate faster in a flip is the tuck, which is the part where you pull together into a little ball. If you want to just do a single backflip in default gravity, you need to tuck into less of a ball, or experiment with tucking at different times. Also consider figuring out a back layout, which is like a backflip without a tuck.
A lot of people look down on random tricking in default gravity because it's easier, but it's fun. Good luck m8, especially if you start to work on tricking in higher gravities. o7