The key to a successful cinder block paint job is applying proper sealant and primer. Whether the surface is in a basement or above ground, cinder block is as easy to paint as drywall once the surface has been sealed and primed to keep moisture out. Moisture will cause paint to chip and flake off, so if the cinder block is part of an unfinished basement, a masonry sealer will be the most important part of the process.
Remove existing paint, if necessary. Use a rubber or metal scraper to remove any flaking paint. Flaked or chipped paint can be a sign of moisture seeping through the cinder block, so be sure to seal the surface if this is a problem. The "This Old House" website recommends using a concrete sealer containing sodium silicate to prevent indoor moisture seepage.
Seal the cinder block surface. Some cinder block, especially in basements, will be treated with a waterproof sealer when the house is built. If in doubt, a fresh coat of sealer won't hurt. Sealer is generally a clear, thin liquid and is applied like paint. Allow to dry according to the manufacturer's instructions.
Prime the cinder block. Choose a primer that's approved for indoor concrete or masonry use. Primers are generally white, but they can usually be tinted the same color as your latex paint to add depth to your wall color. Allow the primer to cure completely before painting.
Paint the area, using a quality interior latex paint or specialty masonry paint. Once your cinder block has been sealed and primed, you can use any type of interior wall paint, so you don't necessarily have to purchase specialty paint. Apply two or more thin, even coats until the desired color is achieved.