Here is how I do it.
I NEVER repeat stay commands.
If the dog does not learn to REMEMBER to stay, the command is useless.
I begin teaching the sit/stay by asking the puppy to sit in heel position. After giving a clear verbal STAY command, and showing the puppy the palm of my hand, fingers together, pointing down, I then hold enough upward pressure on the leash so that the puppy will not move, and pivot directly in front of the puppy so I'm standing toe to toe with her. Keep the gentle pressure upwards. Count to 5, pivot back, release the collar pressure, and at the same time, release and praise the puppy.
Practice in this manner until you can do this, on a loose leash, and count to 30 and the puppy is not moving. DO NOT repeat the word stay. If you have to put her back, once she IS back, you can say GOOD sit, DO NOT SAY STAY AGAIN.
You can reward good responses with gentle low key verbal praise, and food rewards.
Once you can count to 30 while standing in front of the puppy, and the puppy is consistently NOT moving when you move in front, or back to heel position, you can move out to the end of your 6 foot lead. Remember that when you start adding distance, you may end up having to position the dog back again. NO repeating stay. Say GOOD sit, instead.
When you can stand at the end of the leash and count to SIXTY without the pup moving, and when you can go back to heel position by passing around behind her, and you are not getting any movement, you can start introducing distraction.
Distraction can be defined as anything that will get your dog's attention, and cause them to break their stay.
Yep, you WANT them to break. Each time they do, put them back, and praise them for staying. You want to distract a dog into moving a couple of times, and then moderate the distraction slightly so the dog can be successful, release and praise, and then move on to something else.
Don't overdo distraction. The dog has to have the distraction to learn more about the stay concept, but you must not overwhelm her. She needs to be successful often enough so that you keep her interest.
Stay is a precision exercise that takes TIME and PRACTICE for the dog to get reliable, along with creative distractions.