Weeds are a common problem in most lawns, but the extent of the problem can range widely. Lawns with vigorously growing, thick, lush turf don't usually succumb to weeds other than a stray dandelion here or there. The quality of the soil and root depth of the grass is directly related to the amount of weeds in the lawn. Weed a lawn by removing or poisoning them first with a selective herbicide, then build up your grass and soil so you can prevent them from growing in the future.
Wait for a time when the weeds in your lawn have sprouted but have not yet produced any flowers. This means there has been little or no seed production, which will reduce the spread of new weeds.
Choose a still, dry day to pull up the weeds. While moist soil makes it easier to remove weeds, it will also quickly germinate any seeds that fall from the plant during removal. A still day will prevent any seeds from being blown off the plant.
Remove the weeds by hand. Protect your hands with gardening gloves, and then pull them out of the grass. You may need a trowel or fish hook weeder to get under the roots of some of the weeds. Dandelions, in particular, have long tap roots, be sure to get the whole root when you pull dandelions.
Discard the weeds by carefully placing them in a trash bag. This will help prevent the spread of seeds.
Turn over the soil in any bare spots left in the lawn, and apply a granular herbicide to kill any remaining weed roots or seeds in the grass. Choose one that is formulated to kill broad-leaved weeds, which will not harm the grass.
Apply a mixture of grass seed and mulch to any bare spots in the lawn, and water thoroughly.