Smith Grinds are one of the hardest grinds. What you have to do for this is ollie on a surface. Your back truck should be on the surface as should the middle of your board. It's kind of hard to get, and do.
Hints: If your having problems landing the grind on the surface try stalling. Just stand next to the curb, pop an ollie, land the back truck, and the middle of the board 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