Just because you can do something to your dog's hair, doesn't mean you should! There are plenty of very involved procedures that go into creating the shih tzu one sees on televised dog shows. Though most owners keep their dogs in something of a "puppy cut" for trouble-free maintenance, real champion dogs have a longer beauty regimen than many women.
Of course, if you have a shih tzu puppy, the adult coat that requires all the maintenance hasn't grown in just yet. In fact, there is a few weeks when your dog transitions between a "puppy coat" and their adult fur that it seems nearly impossible to keep up with all the mats, tangles and loose hair. However, after a few weeks, the adult coat settles down with all the hairs pointing in the right direction.
Even if you don't plan on showing your shih tzu, there is still plenty of combing to be done. Anywhere from once a week to every three or four days is adequate for companion shih tzus. However, dogs that are kept for show are often combed as much as twice a day to keep mats from forming in their fur that's kept particularly long to drape on the show-ring floor.
Perhaps the most recognizable characteristic of the shih tzu kept for show is the topknot and the many permutations of it. Drawn up into something of a pony tail (or a few) on top of their heads, these allow the dog to actually see while keeping that hair as long as it will grow. Specially made tiny curling irons are then sometimes used in conjunction with teasing to give the topknot volume.
Many people who keep shih tzus for show swear by a few tools of the trade. Most dogs kept thusly are treated to a blow-dry table that allows for hands free operation. Here is where the styling really begins. Some people use special combs that have bristles that bend or spin around under pressure. Most use something to dye the white fur under the eyes that can become stained. Hairspray is often used to keep these follicular masterpieces in place.
The coats of many show dogs differ just enough that a product that works well on one shih tzu may not work very well on another. In fact, the actual composition of the coat (at least in an environment as competitive as the show ring) is a nearly individual thing. Therefore, even related dogs sometimes have slightly different grooming regimens depending upon their coat type.
Conditions for show dogs are so rigorous that even the tap water may be replaced with something else so as to give the fur plenty of shine. Everything you might expect of a fashion model (and then some) is done to shih tzus preparing for the show ring. Most owners wisely choose to keep their shih tzus hair short to concentrate on other things in life, such as working for a living and just petting the dog.