Tape off any areas where you don't want paint to drip. Lay down a painter's tarp or plastic to protect the floor in the room where you'll apply the painting technique.
Place a large bucket of water and a much smaller container of water next to the paint so you have them handy while you apply the color wash.
Wet a rag in the large container of water and wring out the excess. You want the large container to stay clean. Use the smaller container to rinse your rag and apply more water to the paint during the color washing process.
Dab the wet rag into the paint and begin to wash the wall with it. Use the amount of water on your rag to manipulate the paint coverage: more water for a translucent effect and more paint for heavier coverage.
Rewet your rag in the small container of water and add more paint when you're ready. If you need a clean rag, wet it in the large container before you dip it in the paint. Continue this process until the entire room has been painted in the color washing technique.