My favorite, must have grooming tool is my short, curved, rounded-end scissors. I use these for trimming delicate areas (eye and mouth area, paw pads, and rear-end).
A set of quality grooming scissors is essential if you plan to groom your own dog or if you want to extend the time between grooming appointments. You can purchase kits that contains several items or create your own kit. Once I discovered which tools I use most often and which brands I preferred, I built my own kit of all of my favorites.
For examples of shih tzu hair styles and grooming tips, please visit All Shih Tzu.
I recommend finding pic (on Pinterest, etc) of the hair style that you have in mind for your shih tzu to show to the groomer of what you have in mind.