Controlling ants starts outside because even when they make it into your house, their nests are usually outside, and it's better to get them before they make it indoors. There are a number of ways to get rid of ants even when they've managed to infiltrate your house — but you'll need to go directly to the source. The queen keeps an ant colony running by producing ant after ant. If she is destroyed, the colony soon goes with her. The problem is she usually resides deep in the nest and is difficult to find and eliminate.
You can usually trace the ants back to their nest by first discovering where they are getting into your home. Check cracks, edges and seams around doors, windows, trim, etc. Follow the trail of ants back to the nest from there, if possible. You might also locate the nest by noting anthills. When you find out where the ants are coming from, there are products available such as Amdro® FireStrike Mound Treatment, which is formulated to kill fire ants in particular. These are applied directly to the nest. There are also lawn treatments such as Scotts® Snap Pac Insect Killer for Lawns or Amdro® Quick Kill Lawn and Landscape Insect Killer that can be applied to your grass to keep ants as well as other insects at bay for a season.
Ants that are visible above ground or on your kitchen floor, for example, can be removed a few different ways. One simple method indoors is to vacuum them up along with some talcum powder. If you see an ant convoy making its way in or out of your house, sprinkle talcum powder on them and then vacuum. The powder suffocates them inside the vacuum. If you were to just vacuum them up, they could possibly remain alive inside and make their way out after you think they're gone for good.
There are a number of commercial ant-killing traps, baits and sprays available at your local True Value hardware store. Commercial poisonous baits, such as Raid® Double Control Ant Bait and Combat® brand baits can kill the queen and colony. These often can be useful if you don't know where the colony is located. Bait is especially effective because scout and worker ants carry it back to their nest, poisoning the rest of the colony. Sprays are less effective at getting rid of a large invasion because you only kill the ants that you attack with the spray; more are likely to show up later if the rest of the ants from the colony can follow the trail of the first ants. If you aren't being infiltrated by the whole colony, a spray such as Ortho® Ant & Roach Killer can get rid of the individual ants encroaching on your kitchen.
When using a pesticide, carefully read the label and follow all manufacturer instructions. Use it only as directed.