Using Bleach and Ammonia Based Cleaners:
Don't use them. There are plenty of other products out there that are milder and will get you squeaky clean results. Bleach and ammonia based cleaners will discolor your grout lines over time. It may happen very gradually, but it will happen. Try using a mild all-purpose cleaner, or the manufacturer's suggested product, instead.
Scrubbing Tile and Grout:
Never use steel wool, abrasive scrubbing powders, or any other scrubbing material on your tile. Your tile has a finish on it that will be damaged with any of these products. Soft cleaning cloths and mops are usually all that is required.
Letting Spills Sit:
Don't let spills sit for any length of time. The same stains that will discolor your clothes, will seep in and discolor your tile and grout. Oily stains, tomato stains, and drink stains can all sink into your tile, so wipe them up quick.
Not Protecting from Furniture:
Tile is hard and it can withstand a lot, but it will crack or chip if enough force is exerted on it. Protect your tile surfaces by using furniture protectors on the bottom of chair and table legs. When moving furniture be especially careful. Be sure to use protectors on the bottom of any potted plants as well.
Using a Vacuum's Beater Bar:
Don't use them on your tile floors. They may scratch or dull your finish. Most vacuum cleaners have a button that will turn of your beater bar to vacuum hard surface floors like tile.
Infrequent Sweeping and Mopping:
Dirt is the worst enemy to a tile floor. Tile floors need to be swept/vacuumed and mopped regularly to prevent damage to the grout and finish. A quick daily sweep, and a light weekly mopping are usually all that is required to keep your floors looking great.
Not Caulking and Sealing:
Tile surfaces that are exposed to water will need to be caulked. Periodically inspect the caulk to make sure it isn't peeling away from the tile surface.
Similarly, sealing will protect your grout from damage and wear and tear. It also offers more stain protection.
Check your manufacturer's instructions for a recommended schedule for sealing, and the type of sealer you need for your tile.
Oil Based Cleaners on Glazed Tile:
If your tile is glazed, you may notice it can get slippery. Never use an oil based cleaner on glazed or shiny tile. It's an accident waiting to happen.
Forgetting Door Mats:
Most of the dirt that comes into our homes, do so on foot. Be sure to position a door mat outside and inside each surface of your home. You'll catch most of the dirt before it even has a chance to get near your tile.
Over-Wetting the Tile:
Using an overly wet mop, or not drying up spills can damage and stain your tile. Minerals in tap water can leave behind discoloration. Wetness can lead to mildew and dingy grout lines. Floors that are left to dry slowly can have a dull or dingy look. Try hand drying floors to buff and polish them.