After you get it clean it's a good idea to apply a grout sealer to help keep it from absorbing stains - recommended by the guy who installed our tile. It has to be repeated now and then, depending on how much traffic or scrubbing the area gets. The sealer is costly but a quart goes a long way. Get product recommendations from the home store or others that sell tile, or maybe from youtube or other internet sources. I don't remember the brand we used, but it was very wet and runny - almost like water, and the man who did the work just rubbed it on with a rag. You might need solvent proof gloves.