Sweep or vacuum loose dirt from the grout lines
Mix warm water with a small amount of dish soap
Apply the solution to the grout with a sponge or spray bottle
Scrub the grout with a stiff-bristled brush or old toothbrush
Rinse the area with clean water
For tougher stains, apply a paste of baking soda and water
Let the paste sit for several minutes
Scrub again with the brush
Rinse thoroughly
For mold or mildew, use a bathroom-safe grout cleaner or diluted vinegar if appropriate for the surface
Wipe the grout dry with a clean cloth
Repeat as needed for heavily stained areas
Seal the grout after it is completely dry to help prevent future staining