Summarize:

Look for pieces of tile that have chipped or are cracked around the edges. Another good place to start is at any spot where the grout has started coming loose. This is the spot that will be easiest to start removing the tile. If there isn't a chipped tile or loose grout, try to start loosening a tile at one of the ends of the floor, or hit the middle of the tile with your chisel so that it breaks. Try to situate the chisel under the tile at an angle of about 30 degrees so that you can easily lift it from the ground. Use a masonry chisel that's about 1in (2.5cm) wide for best results. As you hit the chisel, the tile should begin to separate from the ground. Continue hitting the chisel until the piece of tile you're working on completely breaks. The tile might not come off in one solid piece, so don't worry if it splits and breaks into smaller pieces as you're chipping away. A small sledge hammer also works instead of a mallet. Move on to the next piece of tile, situating the chisel under the tile and hitting it with the mallet. Repeat this process to lift the tile from the entire floor. Once you remove the first few pieces of tile, it'll be much easier to maneuver the chisel underneath the next pieces. This process will likely take a while, so be patient and go slowly so that you don't injure yourself. Place the end of the chisel right on top of the tile and hit the opposite end with the mallet. This should break the tile, making it easier for you to remove it at a new angle. Move the broken pieces of tile out of the way so that you can reach the attached pieces more easily.
Locate a broken tile or section of loose grout. Hold a chisel underneath the loose tile at a slight angle. Hit the chisel with a mallet to lift the tile from the floor. Continue removing the tiles using a chisel and mallet. Strike the top of the tile with the chisel if it's not breaking easily.