I work on duration first, with me being in front, in heel and on the side. I use a clicker. I do not label it with any word. When starting 'stay' work, I start while in front of the dog, pivot away so my back is to them, Click, turn back, reward. Progress to taking one step, with my back turned, click, turn back, reward. I also working walking around the dog while it remains in a sit or down in both directions. Slowly adding distance, I also jump around, throw bait bags, treats, balls, toys etc while close to the dog.
I do not make eye contact with my dogs, I don't want them to learn that eye contact and watching them like a hawk is part of the exercise or backing away never breaking eye contact. Always click when I am at the furthest point, then coming back to the dog, not clicking when I get back to the dog. If the dog breaks or moves, I reset them, I do not reward them again but go back to the last distance that the dog was successful and reward.
End goal, being able to run away, jumping around like a fool and the dog never breaks the stay, even at hundreds of feet.