People with noticeable drawing or artistic skills as well as color coordinating skills most likely would do great as t-shirt designers
. The usual starting place for most people will begin with a cheap plain white cotton t-shirt and decorate it with whatever is handy. A sharpie in the right artist hands will grab every ones attention, very quickly.
For anyone who has never tried a sharpie on a t-shirt, it is a harder task than one would imagine. The cotton canvas doesn't want to lay still and if you try painting the tee, it could easily become a stiff shirt, very uncomfortable for wearing. Several washing will also help any design fade or disappear. The most logical approach is to create with paper or a regular canvas, then photograph the finished design which can easily and permanently be printed onto a t-shirt of your choice.
If this sounds like designing a t-shirt is too complicated for your fancy, you have some very good viable options available to you. Your design could end up on a website that will print and sell your design on t-shirts. This is websites that hold contests for any artist. It is as easy as finding the websites, submitting your design and hoping yours is picked for the next great t-shirt design.
The process is not complicated. You need to check with the specific sites to see what they need in terms of the quality of the digital image for starters. You will need to go through the application process as well. They all want a little info about you as a person so if they use the design you can be showcased. Some of these guys will judge whether or not they want the design themselves while others will put you design up for fans of the site to vote on.
Anyone with a nack for designs can submit their designs for printing companies or to be part of the fan voting process to determine who the next winner is. The great thing about these sites is that there is always a fresh, new and exciting design just over the next horizon. These companies will either buy the design outright or pay you a percentage of the units that are sold. Either way you could be the next t-shirt design star, with a very good income for your efforts.