The 50-50 is a very easy trick. You should be comfortable riding on the runs before you try this trick.

       First, ride up to the rail with speed, not too much speed or not to little, but just fast enough so your comfortable with it. This is important, because if you sketch out, it could really hit if you fall on a rail. I find that if I go fast even if I'm trying new tricks and I fall, ill be going fast enough so I don't hit the rail with my back, and that could hurt. Next, as your coming up to the rail, bent your knees and stay low. Finally when your on the rail, make sure you stay above it. Keep your knees bent a stay low, this helps you balance a lot. As you come up to the rail, stay right above it. Not, to any of the sides, because you could fall off or hit your stomach or back really hard. Keep your balance as you go across and stay striaght above the rail. Kept holding your knees bent and continue to stay above the rail. I say this over and over because for most of you this will be you first rail trick and it is very, very important. Next, when your about to get off, lien back a bit (like your doing a tail press), or hop off the rail. Just after you come off the rail, spot your landing and try to land there. Just as your about to hit the ground, absorb the shock by bending your knees and ride away clean. Good Luck!