Remember the "mental note" you made to fix that pesky loose floor tile? The next time you step on it, grab a sheet of aluminum foil and an iron and get to work. Most likely, the tile is loose because the adhesive securing it to the floor is no longer sticky. So all you need to do is use a little bit of heat to make the adhesive tacky again to reattach the tile, and then you can check this off of your to-do list.
Place a sheet of aluminum foil over the tile to protect it from the direct heat. Turn your iron to high and place it directly on the foil over the tile. Keep the iron on the foil and tile long enough for the adhesive to melt and reattach to the floor. If it's a small tile, it should take about five minutes; a larger tile might take 10. Finally, place a heavy object, such as a bathroom scale, on the tile until the adhesive dries again.