The way to solve that for the long term is to work on improving your design skills, and the way to do that is to do more art and try new techniques. Watch some YouTube videos on accomplishing certain things with your software. I've been using CorelDraw for around 25 years and still learn new and better ways to do things when I design.
Depending on what sort of designs you want to make, you may get better results more easily with a vector program (CorelDraw, Illustrator) rather than a raster program like PhotoShop. But opinions vary on that point. I use both/either depending on what I am doing.
But don't overcomplicate things for yourself. Simple sells. Many shirts are just text; extra bonus points for using a font and arrangement that is suitable for the idea ... at least half the stuff out there does not. A simple cartoony graphic or tweaking the text to creating some sort of art element can add that extra bit of interest and/or another layer of pun/joke/innuendo.
My best sellers have all been a combination of text and a simple image that taken together have meaning, but would not on their own (both are required to make the joke/idea work). If an idea does not require a graphic, adding something may, or may not, improve it from the customer's point of view. All my current best sellers are single-color prints, though my first was a 3-color print that absolutely had to be 3 colors.
But YMMV. See what works for you.