Determine what size rope you need. Bull ropes are not sized by length or small, medium or large. Rather, the sizes are Pro (for bull riding), Calf or Baby. Calf is suitable for young teen riders, Baby is for kids and Pro fits most adults.
Decide what type of braid you need. There are two basic types, leather or nylon. Bull ropes are made out of poly-rope, not hemp or fiber. If nylon has been added to your braid, the rope will be soft and flexible. If leather is braided in with the poly rope, the rope will be much stiffer. Nylon will also wear longer then leather. Most bull riders want a stiff bull rope because it provides a more stable grip.
Choose your plait. The plait is defined as the number of strands (of material included in your braid) that are then plaited together to form the rope. The higher the number of plaits, the stiffer your bull rope will be. It also will be wider. The plait can be done to make the rope flat or round. You'll figure out your preference as you ride more. You will be able to choose from a 5 plait or a 7 or 9. A 5 plait is the loosest and a 9 is the hardest. Most ropes have two plaits and will be listed as a 9/5 rope, for example. The first number is the plait count in the main body of the rope and the second refers to the number of plaits in the tail.
Choose the tail. This is the part of the bull rope that extends beyond the "handle" that you wrap around your wrist to help you keep your grip. Tails are described as regular (hard), soft, or mush. The number of plaits in the tail determines the type, and it is not unusual for the tail to have a different braid than the rest of the rope. If you are new to bull-riding, stick to a regular tail until you develop your own style and preference.
Apply rosin to the handle. As soon as you buy your rope begin to learn how to take care of it. Bull rope rosin is shaped like a bar of soap. You rub in onto the rope at the handle. When you grab and hold the handle, the heat from your hand will warm the rosin, making it turn gummy. This will make it easier to maintain your grip.