A proper fertilization schedule is important for a thriving green lawn. Fortunately, the good folks at Scotts have good products and information available to guide gardeners through the best types, timing, and techniques for lawn fertilization.
In addition to the articles and product information, they also provide an Annual Fertilization Program Builder, best suited geographically by region. This guide recommends products and the best times to apply them for your particular type of lawn grass.
Also see Scotts general gardening information