Generally speaking, ceramic tile requires little maintenance due to its glazed surface, which is hard and mostly stain resistant. But, what about the grout? If you did not properly seal it when it was first installed, then over time the grout can become dirty and stained. From what I have discovered most general cleaning products you purchase at the store do not work very well for cleaning the grout. The solution to this problem are cleaning products designed specifically for grout. Here, are a couple that you might try and that come highly recommended:
http://thegroutcleaningstore.com/grout-cleaning-kits/
http://thegroutcleaningstore.com/grout-cleaning-products/
Here are a couple of videos that you may find helpful too:
http://coatofarmorgroutsolutions.com/home.html