Plant your back foot firmly on the tail, and have the back wheels locked up against the coping. When you're ready, with one continuous motion step your front foot into position, right behind the front truck bolts, and shift your weight from your back leg to your front leg. Keep your knees bent, and commit to leaning in.
When the front wheels come in contact with the ramp, keep your weight centered over the middle of your board, and try to stay on. You'll reach the flat bottom sooner than you think, and hopefully you're still standing up. If not, jump right back up there and try it again. Remember, it's only scary the first time.