A healthy lawn that is properly mowed, fertilized, and irrigated will generally out-compete most weeds. Here are a few tips for care that will help maintain good health:

1. Never remove more than 1/3 of the grass blade at one time. Cutting too much of the blade will stress the lawn by reducing its ability to make starches through photosynthesis.
2. Mow at the highest height for your grass species. For St. Augustine and Bahia, this is generally 3.5 to 4 inches. Turfgrass weeds need full sun to grow successfully and by shading them with maximum height grass blades, their chances of success are reduced.
3. For a basic maintenance level, it is recommended that a complete fertilizer be applied 2 to 3 times each year at rates in accordance with instructions on the product. The University of Florida recommends a 15-0-15 or 15-2-15 nutrient percent fertilizer.
4. The best way to water an established lawn is on an as-needed basis. When the grass blades begin to show signs of stress, i.e., fold vertically, turn a bluish-green color, or will not recover quickly from foot traffic, it is time to irrigate with ½ to ¾ inch of water. Do not water again until the lawn shows signs of wilting. The existence of patches of dollarweed in a lawn almost always indicates too much irrigation!

Additional Resources
http://edis.ifas.ufl.edu/LH010
http://edis.ifas.ufl.edu/EP236