The 50-50 is probably the easiest grind. The hardest part is finding a slick surface. All you do is go pretty fast then pop an ollie and land on the surface. Both of your trucks should be on the surface. Now, just slide and when you're finished with that pivot off the curb or whatever.
Hints: If your having problems landing both trucks on the curb, try stalling. Just stand next to the curb, pop an ollie, land both trucks on the curb, and pivot off. Do that a few times and you'll be able to do the real grind perfectly.

Trick contributed by: www.skateboarduk.com