You can do this trick standing and riding. Some people like to practice on carpet in their home, but this doesn't work at all. There nothing alike. First, put all your weight on the nose of your snowboard. And try to lien forward as far as possible, but without falling. It might take a long time to get your balance perfect, but after it if really help you with lots of things. Also, when you are leaning forward, do it straight forward, not to a side, but straight forward. Then hold your balance as long as possible and then go back flat on your board.

Good luck!