When i do it, i hold them up to the light and you will see what looks almost like a triangular point at the very end and just cut that off.
on youtube theres a video that shows exactly what im talking about, but even when their really long, you only cut a teeny tiny bit off. Just type in how to trim or cut bearded dragons nails.
if you do happen to cut too short make sure you have flour onhand, this will help clot the blood and stop it from bleeding, but hopefully that doesnt happen!
Ive found dragons nails are exremely harder to cut then dogs, cats and animals of that nature since their so small and you can only take the slightest bit off, but just taking the pointy tip off makes the world of a difference with them scratching you.
Good luck and id definetly check the video out.