If possible get him in a small round yard or arena where he can't get away. To start with just get him used to having things near his head. Hatlers etc. rub your hands all over his face, behind his ears just make sure he is ok with it. The once he is ok with that just try getting him to lower his head by using your thumb and forefinger pushing between his ears or using just the part that goes behind the ears of a rope halter and pushing down until he releases.dto this until you can get his head down near your waist each time. Then with the bridle, put the head piece in your right hand and the bit in your left hand and place your right hand between his ears with your arm resting on top of his neck (this way he finds it harder to pull away but can still move) and place your thumb of your left hand right in the corner of his mouth to open it and gently place the bit inside it. Do the bridle up and wait for him to be comfprtable with it. May take ten minutes or so. Once he seems reasonably comfortable, take off the bridle and leave it for the day.
The next day (or as soon as possible) do the same thing with putting the bridle on but this time leave it on for a little longer. Continue with this for as long as it takes for him to accept it without getting bored. Then put a saddle or lunge roller on him with the bridle and using some baling twine or rubber, tie the bit to the rings on the front of the saddle (we call this tackling up) nice and loose so that if he relaxes there is still contact on his mouth but it is comfortable for him. Just leave him in the yard with this on for around half an hour or so. Do this for about two days. Then jsut put the bridle with no saddle and not tie him to the saddle and get him flexing to each side from the ground. Remember that the second he gives to the pressure, you release. You could also lunge him with his head tackled up. This helps to teach the horse the correct way to carry his head once he has a rider on his back but it doesn't force the horse to do anything.
Walk him around in the bit and stop him, back him up. Start off pushing on his chest as well as pressure on the reins if you need to to get him to back up.
Once he has figured all this out on the ground he is ready to try it in the saddle. Jsut make sure he is in an enclosed area like roudn yard or arena when he is ridden the first few times.
Once he is being ridden the first thing he needs to be taught is to one rein stop in case he does bolt with his rider. It is difficult to teach from the ground but the flexing should help with that.
The rest is just practise.
Hope all that made sense. Just let me know if you didn' t understand it.