If you're planning on staining a concrete floor, the most important step in the process is cleaning. Anything that prevents the stain from penetrating the concrete will mean a less-than-satisfactory result. Grease, oil, dirt, paint and anything else that's not a part of the actual concrete will prevent the stain from penetrating the concrete. Once you have a clean floor, you can focus on finishing it with a beautiful stain.
Sweep the concrete clean of as much dirt and debris as possible.
Hose down or wipe down the floor with clean water.
Rent a rotary scrubbing machine with a pad specially made for scrubbing concrete floors.
Scrub the floor with a trisodium phosphate (TSP) solution. TSP solutions are available under a variety of brand names at home centers.
Clean up any remaining glue, caulk, tar or any other material with a paint scraper. If the material doesn't come off with scraping, try a chemical stripping compound. Be sure to wear chemical-resistant gloves.
Scrub the floor again with TSP, using the scrubbing machine.
Rinse the floor with clean water.
Allow the floor to dry thoroughly before applying stain.