Veileds are very finicky with fast movements - as are most chameleons. The best way to go about it is leave the door open and sit in front of it. Being lower than your chameleon will show submission and he will not feel territorial. Waiting will give him time to feel out the situation and not get upset. Once he has decided to come closer to the door slowly move your hand up to it while sitting down and if he stops, etc. just stay still and let him continue to feel the situation out. If he decides to go back inside and hide then walk away and sit across the room while you do something like watch tv or play on a computer. Some times they feel more comfortable when you are not watching them. Once he has ventured outside pick him up by keeping your hand flat and always at the height of his feet. Slowly start to scoot your hand under him 1/3 of the way and let go the other 2/3rds of the way. Make this a daily routine and you shouldn't have issues when he's older.