How do i get my bearded dragon to like me?

At first when i got him(or her don't know yet) he liked being picked up now i've had him for a week and when i try to pick him up he starts running, and opening his mouth (i dont know why) so if you know why he does that then please tell me, and if you know how i can get him to stop( how i can get him to stop opening his mouth like he's angry, i know the running thing will be grown out of) so basicaly, how can i get him toi like me?