Hi Susan, I'm sure you'll get great answers from the community. You can also find lots of posts on this subject by searching (use the search bar on the top of your screen). Here's a search that I did for "how to clean grout": http://www.hometalk.com/search?filter=how+to+clean+grout . @The Hometalk Team even has a board dedicated to grout: http://www.hometalk.com/b/617458/grout
mr clean magic eraser , the best
Check out this article I wrote
@Susan I find the easiest cleaner to use is the scrubbing bubbles foam spray - requires minimum effort. Takes lime away from ceramic and for tough grout, spray and scrub grout with a toothbrush so you concentrate where the grout is. I have several friends that have used this on old showers after they moved in and they report that it worked ver well. After you get it clean, then spraying with the bubbles once a week should keep it under control.
They also make a paint pen that you can use to re-color the grout.