Two ways, (1) use common salt "ie the salt you use on your chips etc, just pour it on the dandilions,
or (2) use lawn fertilizer in the same way ie pour it on the plant,

or use lawn weed & feed.

If you can remove any heads off the plants "great" this will reduce the risk of the seed heads re-seeding in the lawn.

If you want a chemical answer there is a weedkiller gel that you dab on to the weed.
I haven't used it or read the instructions regarding children and pets on the lawn after application, you would need to do this as its possibly toxic.

I mourn the loss of the Weed Pen, together with the 'deodorant' stick style push up weedkiller, neither of which appear to be produced now. Roundup, though, has a push up gel weedkiller, although the end is quite broad, so I'd imagine you'd have to be very careful not to get it on the grass and just in the middle of the dandelion.

Is having dandelions in your lawn so bad? I have both dandelions and daisies in my lawn and I live with them...to me they are beautiful.....few will agree with me but just my opinion.

I certainly would not use salt. It will kill the dandelions but kill some of the surrounding grass and the salt will stay in the ground for some considerable time stopping grass regrowth .

The simple answer is Verdone Extra ( available at some DIY sheds/garden centres or online.. I'd recommend you buy the concentrate as it works out far cheaper per litre than made up sprays) . You can either water it over the whole lawn with a fine rose watering can (It kills weeds not grass) or you can make up a small amount in a sprayer and spray each individual weed.

I'm a professional gardener and look after the lawns of 35 customers. Those who don't like dandelions/daisies don't have them and Verdone is the thing to use

As Dungy said you can also put a few grains of granular weed and feed onto each weed but don't over do it it as this will either brown the grass around the weed or make the grass at the place where you apply it go much greener than the areas of lawn where you haven't applied it.

For pure weed killing on a lawn( as opposed to weed and feed) Verdone Extra is the answer and it kills weeds that granular weed and feeds don't touch.

I love daisies in my own lawn but spot weed kill the odd dandelion that appears

Inspite of what Anchorman says ref using salt,
ive used it myself for many years its a known and tried and tested method used via victorian gardeners long before chemicle's we're even invented.

If the salt is spread in the centre of the of the leaves they take the salt down to the roots,
the only sign to the lawn will be a brown dead plant,
you then remove it and you can if you feel the need re-sow with seed.

Again google with give you all the verious methods including im sure the one ref salt.

I got to use this method via a gardening book
"TITLED THE GARDEN?
for expert and amateur byE.T ELLIS, f.r.H.A 1934.
I dont think you can argue with this persons advice.

Anchorman's right about Verdone Extra, its a much better lawn weedkiller than the combined Weed and Feed/mosskiller preparations.
On the subject of salt, it will kill what you put it on - but if you use too much or too often, it will 'poison' the soil around it and kill off anything else growing as well.

Several of my customers have added salt to dandelions and most have made a real mess of their lawn. A tiny amount of salt spread carefully on the dandelion will probably be OK but most people over do it and burn the grass around the weed,poisoning the soil and leaving a burned area for weeks or even months .

Why risk it when a perfectly good weed killer designed to kill weeds but not grass is available?

P.S. salt is a chemical!