The most important piece of advice I could ever offer in the way of lawn care is simple. Mow the lawn high. Most lawns should be cut at a minimum mowing height of 2.5 inches, give or take a notch on your mower's adjustable wheels.
A longer lawn will have more surface area for photosynthesis to occur. Increased photosynthesis results in more plant growth, an extensive root system and a healthier plant.
Weeds can be drastically reduced when lawn is maintained at a higher cut. Once turf adapts to growing at increased heights, it fills in and becomes dense and lush, crowding out weeds that normally invade when turf is weak and stressed.
A dense, lush lawn maintained at a minimum height of 3" is more tolerant to infrequent watering and drought stress because there are increased moisture reserves in the leaf tissue and root system. Although your turf will still need water, the effects of drought or water restrictions will be less noticeable and take longer to occur with a higher mowed lawn. This could be the difference between your lawn turning brown or making it until the next rain.
The most noticeable benefit of the longer turf is aesthetics. The increased amount of leaf blade provides a dramatic improvement in turf color. You will notice your lawn become consistent, uniform and lush looking. Shade zones, patchy areas and weak spots will fill in and help achieve a dense "carpet" effect when given the right opportunity.
Your 3" lawn will need to be mowed once a week during the growing season but contrary to popular belief, it will not be more work. Once the grass reaches that uniform height, you will still be cutting off the same amount of grass as you would a lower cut lawn.
Of course there are exceptions to every rule and this one is no different. Some southern grasses just don't like to grow that high and thrive just fine at lower heights.