For those of you invested in the Merch by Amazon business here is a nice resource for you. People without any design background tend to use random fonts on a design, which is poor practice. You want to use typeface to strongly affect people and have them react in a certain manner. Use typography skillfully and you can influence and affect your audience emotions.
In this post is a very cool Periodic Table of Typefaces. This chart displays the most commonly used typefaces in design. Print this out and hang it on your wall. The next time you start designing shirts reference this chart and understand what fonts will work best on your designs.