What are the most effective ways to teach my dog to stay?

Since she knows some commands, ask your dog to sit or lie down. As soon as she is sitting or lying (it's up to you), hold your hand out in front of you like a stop sign. At the same time, say the word "stay." After a second, reward your dog with a treat. Next, release her with the release word you choose, such as "okay," allowing her to move and praise her. Repeat the stay, rewarding again after one or two seconds, then releasing your dog. Build up the length of time you ask her to remain in the stay by a couple of seconds each time. Once you have built up to ten seconds, you can offer treats multiple times during the stay. You can also hold your hand up periodically, giving the stay cue to remind her that she is not finished until you release her. Don't ask for too much too soon. Remember to always reward the stay rather than the release.