first things first, before you start doing what everyone is saying, just find a short one, go fast and launch off and land on it further down the bottom. It will give you awareness of the speed and angle you need to be going at to comfortably hit it. Once you feel comfortable doing this, slow down and start popping off the lip and landing higher up. Above all make sure you practice raising your tips up before turning 90. I'm still learning "urban" style rails, and on occasion I've had one of my tips hit the side of the rail. Above all, just pop off the lip and you should be fine.