Step 1: 
Lay your shirt out on a flat surface. Fold one side of the shirt to the center. Fold back the sleeves as needed to create a straight line down the middle.  

Step 2: 
Fold the other side of the shirt to the center. Your shirt should now be a neat rectangle. If you are working with long sleeves, fold them down the rectangle and back up to be contained within the rectangle. 

Step 3: 
Fold the rectangle almost in half, stopping just short of the bottom.