If the garment gets wet shake it out vigorously then place it on a clothes hanger to dry at room temperature. Wrinkles will generally fall out by hanging for several hours on a hanger. Use a clothes dryer, Tumble dry, no heat setting, for 15 minutes to remove stubborn wrinkles. Pressing on the back side, through a cloth or paper is also helpful. Use no steam and a low heat setting.
Steady pressure is better then too much back and forth ironing.
Store the garment on a hanger and do not cover the garment in a plastic bag for extended periods of time. Use a cloth bag or drape if additional protection is desired.