front-side nose grind
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1. Learn to do nose manuals first (nose wheelies).
2. Approach the ledge at a little bit of angle; don't ride up parallel to it.
3. Make sure you're going pretty fast.
4. Pop a clean ollie, and land on the front truck like you were doing a nose wheelie.
5. Grind as far as you can.
6. As you reach the end of the grind, add a little more pressure on your nose to get that extra pop off.
7. It's a good idea to learn this trick on a ledge that has an end; this will enable you to practice coming off.
There is a great guide available for learning almost every single skateboarding trick in under 8 weeks.