To train to walk backwards away from you, lead your dog into a narrow walkway, like between the bed and a wall, or between a coffee table and a couch. You walk backwards to do it while facing him. When it's time for the dog to walk back, command him with a tiny treat in your hand, 'back....back...back', until he's all the way back where you both started, then calmly praise and give treat immediately. Once he learns it well, it can be done anywhere.
While he's lying down on the floor on his belly, you can teach him to crawl forward without standing up. Put one hand with palm toward him to guide him to stay down while he crawls. Hold the treat directly on the floor as you slowly move it away from him so it's just out of reach. When he's crawled several feet, give him the treat and tell him 'good crawl!'.