Ideally clean your shirt after every wear. Use good quality fabric detergent and softener and don’t use too high a wash. Hang the shirt on a good quality hanger (not those metal ones used by dry cleaners) and allow it to dry naturally.
Once the shirt is almost dry it is ready to be ironed.
Begin with the underside of the collar. Smooth away from the collar points towards the back of the neck. Continue by ironing the front of the collar. Next, iron the yoke area from the neck outwards, and then iron the pleats in the same direction of the fold. Iron the cuffs of your shirt from the inside out as well.
Put the sleeves down flat and iron upwards toward the shoulders. Iron the other side of the shirt sleeve before moving on to the next sleeve. You may find a sleeve board useful at this point. Finally iron the body of your shirt by starting at the top and moving downwards towards the hem.
Do not use wire hangers. If the hanger has firm shoulders, it will prevent unsightly bumps.
Always spray your aftershave / cologne on your body and not on your shirts. Wait for it to dry before dressing, as cologne can stain your shirt permanently over time.