Mow your grass to the proper height. Most people don't mow their lawns often enough and when they do, they mow it too short. This weakens and kills the grass, allowing bare soil areas that increase runoff and weed encroachment. Most grasses shouldn't be mowed shorter than 3 inches.
Instead of bagging, leave your grass clippings on your lawn as natural compost. They decompose quickly and become a natural fertilizer. The clippings release nitrogen into the soil, reducing the need for other fertilizers. The layer of clippings will hold in moisture, reducing the need to water during dry spells.
An excellent alternative is to compost grass clippings with brush, dried leaves and other garden materials.