Ground work, ground work, and more ground work. Get him obeying commands like 'walk', 'trot', 'canter' on the lunge line or free lunging in a round pen. The MOST IMPORTANT command for him to learn is 'whoa' or whatever word you use for 'stop right this instant no matter what you are doing'.
When you are ready to ride, you can use those verbal commands in conjunction with physical cues (leg aids, rein aids) to slowly teach him that saying 'walk' with a leg nudge on his sides means walk on.
But I do agree with others that have said you need a trainer to help you out. An untrained horse and an untrained trainer/rider is not a good combination at all.