Keep an eye on your Shih Tzu and his actions. If your he obeys, you should make eye contact, offer verbal praise and give him a treat in that specific order. An example would be that your Shih Tzu sits - look him in the eye, say “Good boy, that was a good sit” and give him a treat.
Shih Tzu's are sensitive animals. Reprimanding them is usually unproductive. Instead, only offer positive reinforcement when they do good things.
The “stay” command can be taught from three different positions: sitting, laying down or standing. The end goal is to get him to obey the “stay” command from any of these three.
Start with your Shih Tzu on his leash and with you to his right side. Take your hand, palm forward and put it in front of his face, so that he sees it and say the command “stay”. Now step forward on your right foot (not your “heel” foot, which is your left), take a step or two forward and turn back to your Shih Tzu.
Repeat the hand signal and the command “stay” and step back to your starting position at his side. Give him verbal praise for staying (such as “good stay”) and reward him with a treat.
As you progress with the exercise, you should stay facing your Shih Tzu, but not beside him for longer periods of time and then eventually, you should gradually increase the distance away from your dog that you are standing until you are at the end of his leash and standing away from him for a long period of time. Make sure to continue praising and rewarding him for his good efforts.
Remember: This is a very gradual exercise and the distance and length of time you are away from your Shih Tzu should gradually increase.
You may be worried that you Shih Tzu's only motivation for obeying is his treats, but this is not so. Dogs are eager to please their owners. Make sure that for this exercise you are not showing the treat to your Shih Tzu beforehand and you will be fine.
Training is a slow process and as previously mentioned, most Shih Tzu's do not respond well to getting reprimanded. Make sure to “dog proof” your home so that there are less tempting bad situations for your Shih Tzu to get into, but do stick to your guns on the small, important “tricks” you are teaching him. Your Shih Tzu should always be willing to do a “sit” or a “stay” once they’ve learned it and if they aren’t, work the exercise with them more often.
After you feel confident in your Shih Tzu’s ability to “stay” under controlled circumstances, switch up the situation. Have him stay from different positions or in different environments. Allow for distracting variables once you are confident in your Shih Tzu’s training without the distractions in place.