Lay the T-shirt flat on a clean surface
Smooth out wrinkles and align the seams
Mark the desired sleeve line with chalk or a fabric marker
Cut off one sleeve along the marked line
Use the first cut as a guide for the other sleeve
Decide how deep to cut the armholes
Cut the neckline lower if desired
Trim small amounts at a time for a cleaner fit
Check both sides for symmetry
Stretch the cut edges gently if you want a rolled look
Try the shirt on and make final adjustments
Wash the shirt after cutting to soften the edges