Sweep or vacuum your glazed tile floors regularly to keep them from getting dull. Tiles may be resistant to dirt, but sand and grit can dull glazed surfaces. Clean tile with mild detergent and clean water, using a rag or chamois-type mop rather than a sponge mop. The latter pushes dirty water into grout lines and makes them harder to clean. Be sure to change the water frequently while mopping; dirty water equals a cloudy floor.
If your tiles look hazy, you might be dealing with soapy residue. Remove the film with a nonabrasive all-purpose cleaner. You could also try a mild acid -- such as fresh lemon juice -- on ceramic tiles (but never on marble). Rinse thoroughly with clean water, and buff dry with a clean lint-free cloth. Be kind to your knees and dry tiles the easy way: by using your foot to slide the cloth over the floor.
The real secret to a great-looking tile floor is clean grout. Grout is porous and absorbs grease and other stains. Skip commercial cleaners and instead make a paste of baking soda and water. Rub it on the stain, let it sit overnight, then scrub the stain in the morning with a stiff nylon brush (a metal brush will damage the grout). Repeat as necessary. Apply a silicone-base sealer to the grout to repel future stains.