Cleaning the grout first will make tiles look fresher. Sticking transfers onto the tiles with a pattern on is an economical way to brighten tiles. Tiles can be painted with a colored paint of your choice.
If you have ceramic tile that is cracked or broken you can mold a two part epoxy and then said the area lightly to fill the void. Then the tile can be painted with a paint with a high gloss finish similar to that of the other tiles.
The best thing to do is to get CLR and try to clean it. If it does not work you can buy a vinyl floor and lay it over the tile that is on the ground now. That will make it look like brand new and it really does not cost that much.
Take some water, mix it in cement and make a paste and then apply it on the place where you want to fix the tile and thats it. you are ready to fix the tile.