Flooring Tile - ceramic tile & grout

I have a ceramic tile floor in my kitchen and the grout lines have always looked dirty, like theytook on all the dirt when we mopped and I would like to know what can be done to fix tese grout lines or should I say to fix them ? Also in my bath room around the tub and on the wall its hard to keep the grime and mildew from coming back all the time and I would like to know what can be done about this? How long should you wait after you grout to allow water on the or to take showers and get water on grout?

There are commercial grout cleaners available. You can clean the grout with the cleaner and an old tooth brush. In showers, grout sometimes becomes discolored with mold/mildew. Grout is porous and absorbs moisture and becomes a breeding ground for mold/mildew in areas that are dark, damp, soiled, and unventilated. In the shower, the mold/mildew will have to be disinfected with a bleach/water solution. Use an old tootbrush to scrub. Once grout is clean and thoroughly dry, apply a penetrating sealer. Grout that has been properly sealed tends to to absorb moisture, oils, and soil. Wiping down shower after each use with chamois or squeegie will keep surfaces dry and clean and prevent mold/mildew and mineral and scum build up. Leaving shower door or curtain open after showering will allow ventilation into the shower. Running bathroom exhaust fan during and at least 30 minutes after showering will also help. In addition, spraying surfaces prone to mold/mildew with a germicidal spray will help. Occasional disinfecting with bleach may be necessary.