Imagine returning to your home with guests after a formal event. Your Shih Tzu hurries over to greet your guests. Your guests brace themselves, expecting your dog to jump onto their nice formal clothes, but to their surprise, your well-behaved little dog sits and reaches out a paw to 'shake' instead. One of your guests crouches down and gives your pup's paw a little shake. Her face lights up in a big smile and she compliments you on how charming and well behaved your dog is. You look at your dog, feeling proud. You appreciate the work that you have both put into her learning how to shake, and you appreciate your own cleverness, for coming up with the idea to use that trick to train polite greetings.
There are several great reasons to teach your dog how to shake. 'Shake' is an adorable trick to show off to friends. It is a great way to get your pup used to contact with people in a fun and rewarding way. It can prepare her for future harder tricks, such as 'limp' and can help to desensitize her to being touched on her paws for nail trims. It can stimulate her mentally by encouraging memorization, problem-solving, and social interaction. Finally, it is just plain fun!
If your pup is not comfortable being touched on her paws, then you may need to spend extra time getting her comfortable with being touched there before teaching this. To get her comfortable, you can simply touch her paw gently while giving her a treat. Repeat this with both paws several times a week, until she seems happy and relaxed when you touch her.
If your dog has ever shown any form of aggression, and especially if she does not like having her paws touched, then do not teach this trick on your own. Instead look for a qualified trainer in your area, who has experience in dealing with aggression. Work with the trainer first to treat her aggression and desensitize her to touch before attempting any tricks that involve physical contact.
Tricks should be fun for both of you. If you are getting frustrated, then simply take a break from training and come back to it later, when you are feeling happier. If your dog seems to be struggling, then she might need for you to stay on the current step for longer, or even go back one step and practice that for longer before moving onto the next step. She also might need to be praised and rewarded for attempts at the correct behavior, to help her figure out what it is she is supposed to be doing. If that is the case, then try breaking down the training even further for her and rewarding her for smaller steps toward the correct action. For example, if she is struggling to place her paw all the way into your hand during a step that calls for that, then try rewarding her for simply touching your hand with her paw first, and then gradually help her work up to placing it completely into your hand, by rewarding touches that are closer and closer to the correct spot, where she is supposed to place her paw.
To get started you will need lots of small, tasty treats, that are easy to eat. Your dog will need to know the 'sit' command. You will need a calm location to teach this at, and you will need a positive and encouraging attitude, patience, and a willingness to have fun.