I raise Seeing Eye Dogs so I will give you the adivce that we use to get the dogs to come.
First put the dog on a long leash, let her get her mind off of you and just let her run around the yard with no restictions. Then call her name and see if she comes, if not then gently reel the leash in until she is right next to you. Then PRAISE! Repeat this several times, until the dog comes by itself then eventually go off leash. Remeber to always have a high pitch "girly" voice. It helps.
For the stayin in the sit and down position, we use our hands. First get your dog in a sit/down. Then get the dogs attention to focus on you. Then place your hand in front of the dogs face and say stay. Take a short step out, stand there for about 1-2 seconds. Then come back to the dogs side and PRAISE! Repeat this several time lengthening the time that you are away from their side.
If you have anymore questions feel free to PM me anytime.
P.S. Always remeber to use your happy voice when prasising and trying to call the dog in. Use your regular voice when telling a command. It also helps if you pick a side for the dog to be on at all times. Like our Seeing Eye Dogs are trained to be on our left at all times. When sitting, walking, also while laying down.