Lay the T-shirt flat on a clean surface
Smooth out wrinkles and align the seams
Decide how low you want the armholes and neckline
Mark the cutting lines with chalk or a washable marker
Cut off the sleeves along the seam for a basic tank top
Cut the neckline lower if desired
Trim the armholes wider if desired
Cut slowly and evenly
Check both sides for symmetry
Try the shirt on and make small adjustments
Stretch the cut edges gently if you want a rolled look
Wash the shirt to soften the edges if needed