Agree with all the info about minimal handling of your chameleon. I'm pretty new at this too, and understanding there are times you might eventually have to be able to remove him for cleaning I will tell you how I came to be able to handle my aggressive veiled:
First, I did very little with him while he became accustomed to his new home. If I put my hand in there he would hiss and lunge at me. I didn't want to be bitten but I did want him to learn to accept me, so the plan was to introduce my hand without touching him once a day for only a few seconds until he understood that the hand was intrusive but not dangerous. I always kept it below him and within 2-4 inches from him. I wore thin gloves at first because I need to not fear being bitten (he wold full on lunge attack when I put my hand in there and I did not want to reflexively pull away and accidentally teach him that attacks cause removal of hand.) I would stay rock steady while he tried to bite me. then, when he gave up the attack I would remove the hand and leave him be.
I paid attention to the colors I was wearing when doing this as some days he seemed more agitated than others and I believe bright shirts set him off.
Eventually his attacks became less enthusiastic and maybe I'd get a big hiss and just a small lunge. I eventually felt comfortable removing the gloves and only presented the back of my hand as there's no loose skin or flesh there for them to actually grip in a bite and their nose tends to just bounce off the surface of the hand, non painfully.
The best I ever got was reluctant acceptance and eventually willingness to take an insect from the back of my hand if I didn't get too close. This was huge because it meant my hand had something good to offer. We practiced hand feeding for quite a while. Hissing never went away but lunging did.
At about 8 months something interesting happened and he developed a strong interest in leaving his cage. This was our breakthrough because when I opened the cage he one day scrambled right out onto my hand looking to escape! At this point I discovered I liked it better when I couldn't handle him because he was always trying to jump on me to get out every time I opened the door. At times when he doesn't wish to leave his cage I may still het a hiss and a lunge...I wouldn't call him tame or friendly even, but he often will come out on h s own, and when I have to take him out he may do so reluctantly but I don't fear I'm over stressing him, he knows now what to expect.
I hope this helps you, and remember to keep handling to a minimum even when you are able! And slow is key!
