He still looks pretty small. How old is he? Either way, the taming process may take some time. Not every dragon is like this but it's not uncommon, especially with young dragons. Even the calmest baby dragons are a bit twitchy.
Either way, one thing you can do is place your hand flat inside his enclosure and keep it there for a good period of time, maybe 15 minutes. When you do this, make sure he can't go and hide somewhere. Take out all of his hides so that he can see your hand and return them when you're done. During the first few days, keep your hand a decent distance away from him. After a few days of this, start placing your hand closer, then after a few more days, place it even closer. He may still hiss but if he starts hissing less and less, that's progress.
Wear gloves or something in case he does bite because eventually you'll want to place your hand right next to him. If he walks away, don't chase him, leave your hand where it is for a few minutes, then inch a little closer and try again. If he hisses or bites, do your best to not flinch or pull your hand away. Only take your hand away when he's calm. Go slow, try not to startle him and do your best not to put your hand over his head at this stage(you will at some point but for now it might help him feel safer). Try to let him understand that your hands will not hurt him.
Another thing you can try is doing some calm activity near the cage so that he can see you. Read, watch videos on your phone, draw, something like that for maybe half an hour. He'll start to understand that you're not always going to bother him every time you're in the room. Every now and then, calmly talk to him so that he gets used to your voice. This can make him feel more comfortable if you talk to him with your hand in the cage as well.
Do these things every single day, maybe once or twice a day. Give him time to himself so that he doesn't become too stressed. The biggest thing is to never give up. It may take weeks or even months for him to calm down.
Continue to try and hand feed him. If he gets to the point where he's comfortable taking food from your hand on a daily basis, try luring him into walking onto your other hand using a treat. Place your hand on the floor of the enclosure and hold food in front of him. If he does walk onto your hand, let him sit there for as long as either of you can handle. At this point, you probably don't even need to remove his hides.
Once he seems calm enough to handle, pick him up, hold him gently for a few seconds, maybe an inch from the bottom of the cage, then set him back down. If he tries to climb off your hand when you first do this, don't force him to stay in your hand. Let him crawl off and try picking him up again. If he becomes comfortable with that, try taking him out of his cage. Hold him for about two or three minutes twice a day, then increase the time he's out of his cage as the weeks go by. Pet him, let him crawl on your chest and try not to make him feel like he's trapped.
Eventually you'll be able to touch his limbs, stroke his back and pet his head. A very good sign of trust is when you're able to hover your hand over his head without him being afraid.
Remember, this can take a few weeks or even a few months, especially since he's so young. Be as patient as you can and don't give up. All of these things will happen in stages. Pay close attention to him and you'll know when he's ready for the next stage.
