Flip attempt: Backflip or Frontal flip?

Ok... I'm into Parkour lately and I've mastered the basic stuff (vaults, wall run, even Tic-Tac) and i want to go a little more into freerunning, or to say "showing off". I want do start with flips, but I have minor difficulties when I try to make one: In the middle of the jump - I give up, I don't even tuck my legs to get a backward motion. Any suggestions to make it go right? Is trying to do it from a higher ground a good idea? I don't have access to a trampoline so its not an option. Also, is it better to try a wall backflip or a regular backflip for the first time?