Dandelions are considered a broadleaf weed. Best treated during active
growing cycle with a spot treatment. If you use a dry granular form
of weed killer or a weed and feed type of fertilizer, apply it to wet
grass and weeds. The weed control material must stick to the leaves
of the weed plants to be effective. If you spray a liquid, apply it
only on a calm day so material will not drift onto desirable plants.
Dandelions are a persistent weed problem. Each seed head of a mature plant produces thousands of weed seeds that float easily in the breeze. So if anyone in your immediate vicinity has dandelions, you can count on you having them too.
Remember, broadleaf weed killers are broadleaf plant killers. They
do not, for example, differentiate between dandelions and tomato plants.
Apply them only to weeds in the lawn. Be careful not to get the material
onto desirable plants in your yard. Don't apply on windy days where any mist can carry in the
wind to your neighbors prize dahlias. 
Dandelions turn into delicate puff balls that spread the weed's seeds
throughout your garden on the slightest breeze. Once established, its
roots grow down into the soil several inches. If you don't remove the
entire root, the plant will grow back again and again. Removing them
by hand is another option to chemical controls.
Removal steps: If the dandelion has a white seed head, carefully cup
the puff-ball and remove from the plant before beginning the removal
process. Throw the seeds away avoiding disturbing the seeds.
Pulling dandelions is much easier if the soil is damp. Water the area where the dandelions are growing or wait till after a heavy rain. Weeds will slip out of the soil, roots and all, if the soil is wet.
Slip your hand under the foliage. Grasp the foliage of the weed with one hand.
Insert a weed knife (a short-handled gardening tool) into the soil, alongside the dandelion root, with your other hand.
Rotate the weed knife to locate and loosen the root from the surrounding soil.
Lever the tool partially out of the soil; this should lift the root of the dandelion. You'll be able to feel the plant give way. If you can't feel the loosening of the root from the soil, reposition the weed knife and try again.
Be very careful not to break off the foliage and leave the root in the ground. If the top foliage part breaks away from the root, you'll have to pull this same weed again later.
Gently lift and pull the root completely to the surface, removing the plant entirely from the soil.
Shake off any excess soil and toss the weed into your compost pile.
See also: Edible weeds
If you can't beat 'em, eat 'em! Here's a list of common lawn weeds that can, in part, be eaten.
