The first step is to determine how much TOTAL fertilizer to apply each year -- that depends on the type of grass and the percent nitrogen in the fertilizer you choose. Use the fertilizer calculator on the Manage My Home Lawn and Garden Center page (under Ideas & Know-How)to see how much you need.
Then, apply that amount each year. If you fertilize once a year, autumn is best. You can also apply in spring and fall, applying half the total each time. You can split it across three or four times a growing season if you wish. Just don't fertilize during hot, dry weather. I live in Houston. I use a winterizer early Nov., weed-n-feed early Jan and again in early Mar. I follow instructions that are on the bag. In July I add half strength high nitrogen fertilizer (first number) just to green it up. I use Scott's and the weed-n-feed contains atrizine.