The safest way to wash your tee is to hand wash it in water using a hand wash detergent.
Excessive heat can be damaging to your tees. They not only shrink garments, but can also make a print peel or crack.
It’s preferred to use gentle hand washing detergents. It probably goes without saying but do your best to avoid chlorine-based cleaners, or bleach.
Do not ever ever ever ever, ever and some more ever iron on the designs/prints of your T-shirt. Always iron around the prints to get that crisp look.
Turn the clothes inside out before throwing them into the wash machine. Do your laundry with cold water.