Do you spook your horse when you approach him? Here is how to keep from spooking your horse.

[edit] Steps

Don't walk right at him when you enter the pasture. Instead turn to the side and wait.
Walk nearer to him but not directly towards him (if he doesn't approach you). Stay turned to the side.
Let him dictate what you do next. If he backs away, stop and wait. If he doesn't back away, stretch out your arm as if to welcome him.
- If he knows it you can turn to face him, slowly.
- If he doesn't know it exit the pasture.
Repeat the process; eventually it will sink in that you aren't there to pose a threat.
Never sneak up on it. That's just asking for a few broken ribs.
If he's in a stall, knock on the wood to let him know your there, horses can't see directly in front or behind them, their only ways of defence is to lash out and hopefully disable what they think might hurt them unless they can run(which they can't in a stall.)

[edit] Tips

Remember that horses cannot see up to about 4 feet directly in front of themselves. Their eyes are positioned to focus from the side of their heads, so always approach from their side so you know that they see you.
Making a little noise when you approach also makes the horse aware and you to seem less threatening. Whether it’s shuffle in your step, whistling, humming, etc. you will find that it helps. (Keep it to a minimum!)
Never approach your horse looking him straight in the eye; only predators look straight in the eye. This might scare your horse.
Take time to go and visit your horse in the pasture on times when you don't bring him in so that he doesn't automatically equate your presence in the pasture with a workout. sometimes you could just catch him, give him a treat, and let him go again.
Contrary to popular belief, humans should greet horses by blowing into their nostrils and breathing in the horses' breaths. In the wild, horses don't greet each other by holding their hoofs out! They breathe into each other's nostrils.

If he bucks stand back, but don't retreat too quickly. Retreating too quickly will show that you are afraid. Moving backwards is a sign of submission and he will know he can control your movements.
Never approach a horse you don’t know, or without the owner’s permission.
Never take a grain bucket into a pasture in an effort to catch a horse, especially if there are other horses in the area. Horses can be very aggressive over food and may see you or the other horses as competition for that grain.
Don't blow into your horses nostril too hard, if you do, it could be ticklish for him and he could nip you.