Start with a regular fit. It's the most forgiving and the most versatile. You can wear it tucked into jeans, untucked with chinos, or under a denim jacket. It won't scream "fashion statement," but it also won't make you look like you borrowed your dad's shirt.

What to look for: a shoulder seam that sits exactly at your shoulder bone, a hem that hits around mid-hip, and a body that skims your torso without clinging. That's the sweet spot.

Don't go too tight. If the fabric pulls at the buttons or you can see the outline of your undershirt, it's too small. If the graphic distorts around your chest, it's too small. A regular fit should let you move freely without excess fabric.

One thing to keep in mind: if you're between sizes, go up. You can always roll the sleeves or tuck it in, but you can't add fabric that isn't there.