I don't know how much you already know. Plus I reject the editorial "them", and use the editorial "he", meaning all people.
I used to rescue and rehab iguanas, and became good at taming adult igs, so this information is exactly how I trained even adult igs. Of course, with fearful adults, I needed to use wire yarn Kevlar gloves and arm sleeves. Even then I donated flesh and blood to the cause. But igs under one year old can't hurt you much. Also I attended this forum for the decades of it's large group of expert sdvisers.
It absolutely normal for un-tame igs to violently resist being approached and handled. Turning black is normal for many igs. That is why taming is best if finished before their first birthday. After that, their defensive weaponry gets too powerful and most tamers can't really deal with it anymore. But as I said, older igs are perfectly tamable, but for rare exceptions.
His head-bobbing is to him as your voice is to you. he is communicating a warning to you to stay away, or is saying that he is big and dangerous. Too bad, but we can't let him have his way.
His clinging to your hand is just a reaction of fear at this new experience. He feels like he's falling. It's best to hold him with both hands to give him some footing, and set him down with both hands.
95% igs can learn to trust their handler, and even run to him for protection when the doorbell rings. It may even be possible to train yours to poop in your toilet.
If he discovers his reflection in glass, mirrors, or chrome, he may react with curiosity, but many react with a persistent, inflamed and violent need to drive the interloper out, and get a long-term general bad attitude. IMO cover all places where he might see his reflection.
First, his habitat is his own territory (he is obligate territorial and non-social), and he instinctively reacts negatively to any invasions. It's in his genes. In his natural state he needs no social interactions at all, except once/year when he goes into sex mode, and that's only for sex, and not for company (breeding males are NOT NICE to their mates, and females just take it). If he's a male, he will eventually need a green stuffed sex toy. You have to train him to learn to oppose some of these natural inclinations.
He may never accept you inside his territory, but that's OK, it's not necessary that he does. What you hope for is him making it relatively easy to fetch him out for baths, cage cleaning, etc. Likely, he will come out on his own when you open the door.
Right now it's more important to get him out of his cage quickly than it is to try to train him to not resist. Once he's out, he's in neutral territory where he can learn to accept handling.
Never get him a cage-mate. Even an iguana in another room will likely drive him crazy. This reaction is widely reported.
Practice grabbing him as quickly as possible, no matter how much he hisses, runs, lashes, or bites you. No slow approaches. He is too young to hurt you right now, and as long as you don't break his tail, there is almost no chance that you will hurt him during the 4 second chase.
The quickness is what saves him from most of his anxiety. The more he can evade you, the more he panics. Once you have him, use both hands to press him into your belly. His writhing will stop within 30 seconds.
If he snout-bashes against the walls while he is avoiding you, it is even more important to grab him very quickly. A good trick is to throw a large towel over him. Then pick him up, towel and all.
Take him to a comfortable chair or sofa, holding him firmly with both hands. One hand on his shoulders and one on his hips, so he can breathe. Do this four times/day if possible, in 20 minute sessions. After several sessions, loosen your grip a bit until he tries to lunge away. Clamp down again so he can't escape. Slowly increase the times of softer holding, and he will learn to sit still in your hands. He will feel rewarded with more freedom as you can more and more relax your grip, to the point where he can sit still, free of your grasp.
Try to never let him escape during this process, as he will remember it for years, and it will be harder for him give in to you.
Reward him for being held. Use a warm towel, and treats ( 1/2 grapes, bits of banana, bits of pizza crust, or whatever you discover he really reacts to, on the end of a short skewer so when he takes it he won't bite your fingers - some igs grab treats violently, others, gently), When he learns to take treats, he has come a long way. It could take two months or more, but don't give up.
Eventually he will stay on your lap with no holding at all. Now he is much more relaxed. Now you must let him climb off your lap and explore.
Ig-proof his roaming area, and let him roam under close supervision. Soon he can roam without close supervision, but the typical house has many dangers such as hiding places - cracks between cabinets, access to the inside of upholstered furniture, behind heavy entertainment centers and bookcases. He can pull books down on himself. He may leap at the screen in an open window, push it out, and escape outside. He may climb the clothing in closets and hide there for days or longer until he expires. Escape into a garage is practically a death sentence unless you live in Brownsville TX or southern Florida. Where kitchen cabinets come together at 90 degrees, there is often an opening in the toe-kick space there. Feel all around in that corner and block the opening.
Pins, needles, coins, dice, rocks, potted plant dirt, paper, and other objects he finds will be eaten. Soon he will be able to swallow a peach pit.
Set up a warm zone for him to rest in your living area, somewhere out of the way but in clear sight. He will learn to use it. Hanging a CHE and UVB over it is a good idea if he wants to stay out for longer periods. Hopefully he will train himself to go back to his habitat when he is done roaming.
Your living areas have cold drafts close to the floors. Plus the indoor climate that is comfortable for you is way to cold and dry for your ig. He can spend some time there, but not hours. A simple unobtrusive ramp 6 ft. up to an elevated shelf, with a warming CHE over it, is the healthiest place for him to hang out when he is not busy exploring. He may choose his own perch, like the back of a sofa. A perch near a window is good for him, as all igs like to watch outdoor scenery.
The book "Iguanas for Dummies" by Melissa Kaplan has all the information you will ever need.
I have more information if you want it :-)