Because he's young and unbroke, and I don't know how much experience you have, I want to be careful to say you shouldn't do this if there is a chance he could get away from you before you get the blanket secured... I would desensitize him to it while closed in his stall if possible and with you holding him really securely. With it just laying on him, rub and pat him and get him used to how the straps will feel, but you can pull it back off him if you think he's gonna go ape, and start over slower. Once you decide to start fastening straps, you're committed and you should work quickly. Do one of the chest straps, belly straps fairly tight around him so he can't get a foot through them (they should be crossed if there are two belly straps) and do the stretchy back leg straps last. Then he's secure and you can turn him out in a secure paddock for him to run, roll, and try to buck it off if he will. He'll get used to it once he knows he can't get rid of it. If he gets away from you before it's completely fastened, it is much worse, and he might ruin it before he stops.
How well he takes to this will be a good indication of how easy he is going to be when it's time for him to be backed...
Okie ever wear a blanket? He took to his well.