Horses spend a lot of their time tied up, so it's important that they learn to do so patiently. It's also important that you follow several basic safety rules, because a tied horse can easily injure himself if he panics or tries to escape.
Always tie your horse with a halter (never by the bridle) and use strong rope that isn't frayed or rotten. Tie him in cross ties with panic snaps or to a solid post or ring using a quick-release knot. Never leave a tied horse alone - he could get into a lot of trouble in just a few minutes, including flipping himself over (rare, but it happens).