To enjoy your shirt a long time some tipps for ironing in the following:

Before iroining the shirt should be humidified. Then stretch collar and cuffs to prevent washing shrinkage. When ironing the collar, iron the reverse side first, then the up-side. Begin to iron from the seam of the collar to the edge and from the edges to the middle to avoid pushing surplus fabric into the edges of the collar. 

Important: stretch the collar to prevent washing shrinkage. The cuffs should be ironed from the inner to the outer side while stretching them as described before with the collar.