...follow the washing instruction carefully for each shirt.  By doing that you will increase the life length of the shirt, and decrease its negative impact on the environment.

...washing, unbutton, turn up the collar and turn the shirt inside out. Use light program, 30 °C or as stated on the instructions.  We don´t recommend tumble drying and never to leave the shirt in the machine after the finished program, it might cause wrinkles.  When washing delicate clothes choose a mild detergent.  Wash light colored shirts and dark or printed colors separately.  

...washing, for best results hang the shirt on a hanger, button the collar.  Stretch the cuff, collar and front softly and allow it to drip dry.

...with a light ironing that will give the shirt that extra crisp touch.  When ironing the cuffs and collar lower the heat setting and iron gently.

...your clothes instead of treating them as interchangeable – always consider repairing before replacing.