Summarize the following:
Find a flat, smooth surface, like a laundry table. Position the shirt in the middle of the surface with the button-side (front) facing down. Stretch out the sleeves to each side. Make sure that the edges of the shirt do not fall off the sides of the surface. Fully button up the shirt from top to bottom. Button up the cuffs as well.

Summary:
Lay the shirt on a flat surface.