One rather basic thing to realize. You may not ever "tame" a cham. I think the word tame (or possibly the term "domesticate"
implies that the animal accepts the limitations and environment humans impose upon it and changes their physiological as well as behavioral responses to respond to human wishes. This to me implies we're talking about a social animal like a dog or horse. Most reptiles are not very socially sophisticated and just can't or won't respond in the same ways. You can teach your cham to tolerate you (by hand feeding and sticking to a routine so the cham knows what will happen when you appear). Chams won't be quick learners...they just aren't wired to be good thinkers. In the wild they didn't survive by their wits, but by their physical adaptations. This isn't to say they are stupid, their intelligence is just different. Anyway, you can condition a cham to react to a stimulus such as a treat offered by hand, or being taken to a favorite spot in the house to bask. Once the pattern is repeated enough the cham will accept it and react to it basically the same way. You can teach them to accept a new food item the same way. Or, experiment with different colored shirts...many chams react to certain colors their keepers wear.