Most designs start on a rectangle: a square canvas, a poster, a logo on white. A garment isn't that. It's a small set of curved flat pieces that get sewn into something three-dimensional and then worn by a body that moves. A design that ignores this looks fine on screen and wrong on a person.
Start from the panels
A tee is four pieces: front, back and two sleeves. A hoodie is seven. Before drawing anything, look at the flat shape of each piece, where the edges are, and which edges get stitched together. That's your real canvas.
Decide what crosses a seam
Where two panels meet, a pattern can either run through or stop. Running through is the strength of cut-and-sew: the design is printed on flat fabric before it's cut, so a wave or a stripe can continue from the front onto the sleeve. It also takes planning, because the two edges only match if you designed them to match. Pick the two or three seams that matter most and make those line up. Let the rest be quiet.
Respect the zones the body uses
- Underarm and side seams. They sit in creases and move constantly. Keep fine detail and faces away from them.
- The neckline. The collar area is cut away and stitched. Anything important placed there gets lost.
- The hem and cuffs. They fold. Leave breathing room or put plain colour there on purpose.
Leave extra at the edges
Fabric is cut and sewn with a little tolerance. Extend your background past the cut line so a sliver of unprinted cloth never shows at an edge. Print past the edge, cut inside it.
Think in layers
Keep three things separate: the background pattern that covers the panel, the main artwork that holds the design, and personal details such as a name or number. When they're separate, you can change a name without touching the artwork, and the same artwork works across every size.
Check it on a body, not a screen
Before you finalize, imagine the shirt on someone raising an arm. Where does the pattern fold? What happens at the shoulder? A flat proof can't answer that, but asking the question catches most problems.