Establish the rules beforehand and stick to them as Horse has many variations on the base game.
Create an order for the players either alphabetically or by shooting for the order of play.
Call the shot. Verbally call out what shot you are going to take before taking the shot; unless you are not going to use any props or make any special moves.
Shoot the first shot within the established rules. Once your shot is made, the next player has to make the same shot or they are assigned the letter H.
Shoot the next shot. If the second player makes the same exact shot as you, then it falls to the next player and so on until you are up to shoot again. At that point you, as the original shooter, take another shot.
Shuffle the order. If you're shooting first and miss, then you proceed to the back and the player next in line becomes the leader and gets to decide on the shot taken. If that person misses, then control proceeds down the line until it returns back to you.
Assign the letters. As each shooter misses he earns the next letter in the word Horse. When you reach H-O-R-S-E, you're out.