Training your dog to walk backwards is not only a cute trick, but can come in handy. Imagine your dog being able to back out of the way when you are coming through the door with an armload. Keep in mind that it's not natural for your dog to walk backward, his nature is to turn around and walk forward. But, as with most types of training, the more fun you make it for your pup, the faster he will learn.
When your dog walks backward, he is also exercising different groups of muscles than he uses to walk forwards. It can also help him to develop different levels of coordination. While training your dog can be challenging to be sure, keep at it and he will soon figure out exactly what you want him to do.
Bear in mind, your pup loves to learn new tricks, and the more fun you can make the training period and subsequent play, the more your pup is going to love doing so. You can use just about any command you want for this trick such as, 'reverse', 'back up', or simply the word "back" for this but be sure that you choose a command that is easy to use and stick to it. The last thing your pup needs is being confused by different commands being used for a single activity.
As with any type of training, you need to find a quiet place to work, plenty of patience, and the ability to work with your pup at least a couple of times a day during the training period. The more time you have to practice, the faster your pup will learn to shift into reverse when you tell him to.
The good news is that you really don't need much in the way of supplies to train your dog to walk backwards. You will need his leash, a bunch of his favorite treats, your pup, and if you use one for other training exercises, a clicker. The most important thing you need for this trick is a nice quiet room or spot in your yard to practice. Since this movement goes against your dog's nature, you will need to be patient and ready with his favorite treat when he gets things right.