If you shop is typical, then printing shirts is your bread and butter. But there are many other substrates that can be profitable to your Screen Printing business.
Texsource supplies inks, equipment, and accessories to most of our customer who will probably only ever print on t-shirts, hoodies, and jackets. One thing to keep in mind, however, is that your press can actually do much more. I should qualify by saying that your press, with certain additional hardware, can likely do much more than just shirts. Printed sweatpants are hot right now, especially athletic, gymnastics, school and college related logos. To print sweatpants, you will need a pallet that can work with them. You can get a smaller pallet for printing, say, a pocket logo; or you can buy a larger one and print all the way down the side of the leg.
The ability to print on surfaces other than cotton or polyester fabrics are there as well, and usually will require additives or additional equipment. You can print on glass, nylon, plastics, etc. by adding Nylobond to your ink. This will harden the ink fairly quickly for much better adhesion to these surfaces. Umbrellas, some hats, plastic promotional products, and more can be printed this way, expanding your business opportunities.
How about printing on wood? Wood panel printing is fairly popular in the art community and is easy to do. It requires no more additional equipment than you are likely to have, since wood can easily be run under a typical dryer without scorching or burning (unlike nylon, which typically has to be run through much quicker and under lower heat to prevent burning.
Many shops we see offer services in addition to screen printing such as trophies, engraving (either cutting or laser), vehicle wraps and lettering, embroidery, banners, sublimation, and more. All of these services seem to work together for the screen printer, and can expand your offering to your customers!