It takes only a momentary attention lapse to find out how much paint a freshly opened can of paint contains. Spill the paint, and you're instantly aware, especially if you've not taken appropriate precautions before opening the can, such as moving it to a safe place. The difficulty of removing a paint spill increases with the amount of time you leave it, so don't wait; by doing so, you'll also reduce the chances of someone walking through it.
Blot up as much of the fresh paint as you can, using absorbent rags or paper towels. Use a dabbing motion -- don't wipe, or you'll spread the paint and make the removal job more difficult. Start from the outside of the spill and work your way toward the center.
Mix a solution of warm water and dish detergent to wash off the residue. If the paint is fresh, you should be able to remove most of it, even from carpet.
Moisten old paint by wetting it down with the soapy solution until it's soft enough to scrub off. You can also use isopropyl alcohol to soften old latex paint, but test it first on carpeting to make sure it doesn't fade the color. If you find it's safe to use, put some on the paint, cover the paint with plastic, wait an hour for it to soften before scrubbing.
Once oil-based paint cures, so you may need a strong solvent to soften it. Strong solvents can harm floor finishes and carpet colors, though, so try steam and mechanical removal first.
Blot up as much of the spill as possible, using absorbent rags or paper towels. If the paint is already dry, chip off as much as you can with a blunt knife or putty knife.
Steam carpet stains. One way to do this is to set an iron to the steam setting and hold it directly over the stain. For delicate carpets, it's probably safer to put a towel on the stain; place the iron on the towel and leave it for a minute or two.
Avoid steam on hardwood floors. It can damage the finish and the wood itself.
Soften a stain on a hardwood floor by moistening it with mineral spirits and covering it with plastic for an hour. Mineral spirits won't damage most floor finishes; if it doesn't work, try naphtha or isopropyl alcohol, which are both generally harmless to finishes. If you need a stronger solvent, dab acetone on the paint with a cotton swab.
Chip and scrub off as much of the softened paint as possible, using your fingers, a razor knife or an old toothbrush.
Removing Paint From Concrete
Because concrete is porous, you may not be able to remove an entire spill by scrubbing or using a solvent. Use paint stripper -- it works quickly and it won't harm the concrete. To give the stripper time to work, mix it into a paste made with diatomaceous earth and trisodium phosphate. Spread the paste on the residue left over after you've blotted up the bulk of the spill and wait for a few hours. After the stripper dissolves the paint, it should wick into the paste, and when you scrape up the paste and rinse the area, the stain should be gone.