Some people design in a very organized, clean clear precise fashion.
Some people journal to get started. Some doodle. Some google.
Describe how you get started, it doesn’t need to be shirt design, it can be any project.
You can explain it, or just post a gif…
When I get started with an art project… I would best describe it this way.
I start with brainstorming. I have major undiagnosed/untreated ADD (probably ADHD), and if I don’t write down ideas as they flash across my brain, they’re gone forever. I’ll usually send myself an email with little bits and pieces of ideas. Then I go to visuals…what can I actually communicate visually? Does it need text? Then it’s image research and sketch time. Then over the sketch I try to do a more finished piece.
My background is mostly in stencil design & street-art stuff when NOT messing with digital stuff. I lost my studio access when covid hit though, and I had to learn to use Autodesk Sketchbook on a borrowed work laptop (thankful for that at least) to keep creative. So I haven’t hand-cut a stencil in over a year, but I’ve found Woot derbies to keep me having fun with art.
As for a Woot style? I have none. I’ll draw whatever I think will sell (and I’m usually wrong) 
Oh, and because most of the stuff that does well at Woot is so far away from my own personal taste & “anti-style,” I try to sub as many designs to derbies as possible, because I have no idea what will do well. I’ll have what I think is a sure-fire design that ends up with the least votes, or one that was a 10-minute throw away design that outperforms all of them. I know that subbing tons of designs grates on the nerves of some of the other artists, and I’m sorry, but it’s often my only way of standing a chance.
Whew…that was cathartic.
You sound like me… about 15 years ago! LOL
I keep a journal with me most of the time, even if it is a tiny wallet sized notepad… Never know when something will hit me funny.
I typically start with one thing that makes me laugh, usually a punny title. Then I draw a massively rough sketch. I’m talking like a 4 year old with a crayon. Then piece by piece I draw and refine until I’m happy with that section. Lastly, I color it in and add fine details. Well, fine for me. I usually end up with pretty much “coloring book style” drawings. I don’t get into FINE ART styles unless I’m purposely mimicking something.
That being said, I find a lot of inspiration in trying to mimick a particular style. If you look at my catalog, I’ve tried Berenstain Bears, Dr Seuss, and a whole slew of other styles. It keeps it fun and challenging for me - it REALLY helps fight burnout and discouragement.