The Shih-tzu needs plenty of coat care. He has a doubled fur. That is a soft Undercoat and a wiry outer coat. And that fur continues to grow. To ensure it remains nice and without tangles is necessary to brush your dog every day. Especially if you decide to keep it long. If you do not have time or don't want to , you have to visit the groomer.  Every two to three months  to give him a short cut. But also then to the day brushing a must. 
For the daily care of your doggy there are a number of things you really need. A small curved scissors with blunt points. For cutting the rubber bands that you used for the tail and the feet to the mustache and cut it. 
Wide tooth comb, fine tooth comb and soft brush and a pair of tweezers to occasionally the ears to free up hair. You first comb with the wide toothed comb and looks at whether there is no tangles. Watch specialy behind the ears and under the armpits. These are places where tangles can arise quickly. Then comb again with the fine-toothed comb and brush him finally after with a soft brush. We have a lot of brushes tried but the best in our opinion is the ActiVet..
After that it is necessary to clean the eyes. I use mostly a vanity disc with boiled water when cooled down. If need be you can also use a eyecleaner. Of course also the ears just check and cleaning with a make-up pad and if necessary get there from earlotion hair with tweezers and finally the feet around to cut if the coat is too long. The feet I cut about once a week. Here I use a small pair of scissors with blunt points.
Every three weeks (sometimes more often if they get dirty) the dogs have a bath. We use a delicious dog shampoo Artero's and then as they towel dry rubbed a Artero cream lotion. Especially for Shih-tzu. Never use a human shampoo, not even a baby shampoo. The ph value of a dog is very different from a human being. This can cause irritation and itching.