The goal of teaching your dog to “leave it” is to protect him or your valuables. There are many things that don’t belong in your dog’s mouth. Whether it’s harmful or not, you probably don’t want your dog to eat certain things of yours, and this command can also hinder the investigation of something that he doesn’t belong in.
If your dog has already picked up something in its mouth, use the command “drop it” instead, which will also have to be taught. “Leave it” is important information for your dog to know; it lets him know what’s acceptable to chew on, eat, or investigate.
One method of teaching this command is by using the dog’s curiosity to your advantage. Leash your dog and allow him to play with a favorite toy for a few minutes. When she is sufficiently distracted, throw a new item into her field of vision. Most dogs will show interest in the new item and want to check it out.