Try not to take Jamest0o0's response too personally... We get alot of new keepers on these forums who saturate the forums with posts about how they just want to hold their cham but it wont let them and such.
Try to remember that chameleons are a prey item to any animal larger than themselves, such as humans. They dont have the mental capacity to realize instantly that you arent going to hurt them. Like James stated, they are not social animals so handling, petting and such doesn't benefit they at all. If the cham cant get away or feels cornered, they hiss and lunge at the perceived threat. If that doesnt deter the threat, they bite.
With my veiled, I ignored him while doing cage maintenance and I only handle when he comes out of his cage on his own. He usually climbs out and on top of the cage and proceeds to try and climb the picture frame next to his cage. At which point I scoop him up slowly and move him to his freerange for a little bit.
I never remove him from HIS territory unless absolutely necessary