How long have you had him? Some bearded dragons are more defensive than others, so even if this is your third beardie, he can be a different experience.
Things you can try:
- Cover 3 sides of the terrarium with black construction paper so s/he feels more secure in their environment.
- Place a dirty shirt (worn at least 2x without washing, or a shirt you wore while exercising) inside the enclosure so s/he can get used to your scent.
- Rest your hand inside the enclosure and let it sit there for 5-10 minutes at a time. (Get a book, this can be boring.) Do not attempt to hold the dragon until it regularly walks across your hand.
- Start with short handling sessions (3-5 minutes at most), but don't return the dragon to its terrarium until it is calm.
- Gradually increase the length of handling sessions up to 30 minutes.