Choose your printing method. Will you use an online service or print the shirt yourself? This step will help you determine the materials available to you, as well as the dimensions within which you have to work. If using a do-it-yourself print service such as Zazzle, Cafepress, or CustomInk, you will need to check the format guidelines on these sites to determine the maximum size of your working area and the minimum resolution, or "dpi."
Measure the area of the shirt you want to design for, if you will be having the shirts printed yourself, or write down the workspace limits defined by your print service. For example, if you want your design to cover the front of the shirt from the collar bone to the belly-button, your resulting measurement might be something like 12 inches long by 7 inches wide. Most do-it-yourself services online have templates you can download to use for their products, so look for a "Help" or "Design Guide" link.
Launch Paint Shop Pro and click on "File > New." Enter your measurements into the "Width" and "Height" fields and select "Inches" in the "Units" menu. Enter the resolution required by your printing service, or the print default of "300" into the "Resolution" field. Tick the "Transparent" background selection box and click "OK."
Add your design elements using the vector drawing tools, using new layers for each element by clicking "Layer > New Vector Layer." Keep the background color of your shirt in mind as you are designing, and avoid using layer effects such as transparency or alpha channels that will not transfer to the finished design.
Insert pre-existing graphics or photo elements into new raster layers. Do not add raster elements to your design that are not the same general resolution and do not enlarge or stretch elements to accommodate the dimensions of your design, or they may turn out pixelated and fuzzy when printed.
Add typographic elements or text. Be sure to use vector text only by selecting "Vector" from the "Create As" menu in the text options toolbar.
Click on "File > Save" and select a file type of .PNG, .PSD or .EPS to preserve transparency and quality. Do not flatten the image prior to saving it. For online services, this file is ready to be uploaded and previewed.