Couple tips on doing Smith grinds, you wanna approach with the same speed that you would a feeble and you're doing the exact opposite, as opposed to grinding on your back peg with your front tire on top, you'll be grinding on your front peg with your back tire on top. With the Smith grind you wanna hop on and you really gotta get the back end up and over onto the ledge. So you wanna focus on your front peg and make sure that you're really putting it on that ledge and making sure that you're kicking over the back end so that as you grind what will happen is naturally the back wheel is gonna follow the front one off the ledge.
So depending on how far you plan on grinding or the obstacle you're grinding, you wanna grind and if you can grind off the end that's always nice, but often with Smith's you can get the front end off but you can't really get the back end off, or you can't ride off the ledge. So what you're going to have to do is either kick the back end off so that you kinda come off the grind itself in almost like a toothpick grind where you're just on the front and letting the back kinda hang, or you're gonna just hop both off at the same time, you know, spot your landing, make sure that you land both tires flat, you wanna level out right before, land both tires ride away clean and that's how you do a Smith on your BMX bike.