Dogs enjoy exploring their environment naturally by sniffing all around the area, digging, turning things around and running away with little objects. A training session is best done when you keep your dog away from other distracting voices and people. A clear yard without any little objects is the best idea for such a purpose.
Be sure to take full advantage of any spontaneous behavior you see. For instance when you notice the dog coming at you, give a voice command along with a hand gesture to reinforce this behavior. Try to use a word and sign that you don't normally use during your teaching sessions.