Prior to spreading turf fertilizer, the grass should be freshly cut. Mow the lawn, setting the cutting height between 3 and 4 inches. Taller grass is better able to cope with adverse conditions such as dry spells.
Read the manufacturer's label carefully. Put on safety glasses and gloves. Fill a spreader about three-quarters of the way. A full spreader may accidentally spill fertilizer over the side, creating overlap when applied.
Push the spreader at a steady pace, walking steadily behind it. Do not walk briskly or too slowly; your gate should be slower than your normal pace, but not so slow you apply too much fertilizer over the grass. Too much fertilizer, especially turf fertilizer, will burn the grass.
Make one pass over the lawn in a horizontal or vertical direction. Do not cross the direction the other way, or too much fertilizer will be applied. Simply go from one end of the lawn to the other, turn and repeat until the entire lawn has been treated.
Water the grass according to the manufacturer's directions. In general, this is about 1/4 inch of water -- just enough to coax the fertilizer into the soil, but not cause it to run off into street and storm drains.