Edge Catching Problems During Take-off of a kicker snowboarding?

How do you take off of a jump to spin in the air? Everyone always says to jump off of the lip of the jump using your toe or heel edge while keeping a flat base, but how are you supposed to jump using your edge keeping a flat base? Whenever I take off of a jump on my toe or heel edge, I just end up cathing an edge and landing on my face. Any advice? I really want to be able to rotate off of a jump!