Difficulty: Easy
This is a very useful trick to teach your dog, and one that will condition him for more advanced tricks later on. A good practical use of getting your dog to back up is for tossing him a toy or treat to catch. You can also have your dog back out of the kitchen while you're eating, for example. Teaching your dog to back up will pave the way for more impressive tricks later on, such as incorporating it into a dance routine. Tricks like that are extremely hard to teach, and take lots of time, but the foundations for them start here. Think up creative ways to use back up with other tricks for a much more impressive show.
Step 1: With your dog standing facing you, walk forward toward him. When he takes a step backwards, click and treat.
Step 2: Continue stepping forward. When he takes multiple steps backwards, click and treat.
Step 3: Practice this until he understands that if he backs up, he deserves a treat. Start walking toward him less. You can use a signal instead (Try waving the back of your hand toward him, or taking a single step forwards).
Step 4: Once he has learned this, say "Back" as he backs up and as you give the hand signal. Do this several times until well learned. Remember to click and treat when he cooperates.
Step 5: Give him the command and see if he'll back up! Click and treat well each time he obeys. Reinforce with extra training sessions.
OUR EXPERIENCE
Teaching Caspian this trick was pretty straightforward. We would walk towards him, and click/treat when he would back up. Sometimes he would try and move out of our way instead of backing up, so we decided to relocate to our upstairs hallway—so the walls would constrict his movements. When we moved toward him in the hallway, he had no choice but to back up. He soon got the idea, and we then attributed the command back up along with the hand signal. We usually use the "back" command for him to backup and sit before tossing him a treat or toy.
TEACHING TROUBLE
My dog won't start backing up unless I advance toward him. That's where the signal comes in. Try using the signal as you walk toward your dog each time. Then, gradually stop walking forwards, but keep the hand signal. Be patient and give your dog time to think about it. Also, remember to take enough breaks and don't wear your dog out. Short sessions are the most successful!
Tip: "A narrow hallway or a place where movement is restricted can help in teaching this trick."