For the novice, cutting ceramic tiles to fit is one of the more difficult tasks required in a do-it-yourself tiling project. However, with some practice and the right tools, you can cut ceramic tile without chipping most of the time (you'll always have a few chipped tiles). Keep in mind that not all ceramic tiles are the same. Porcelain, for example, is a very dense form of ceramic. Consequently, porcelain tiles are more difficult to cut without chipping.
Purchase a good quality ceramic tile cutter. You can find inexpensive cutters for a reasonable price; however, you should be willing to pay a few dollars more since a good tile cutter will mean fewer chipped tiles (thus saving you money in the long run). Some tile cutters have features that allow angled and circular cuts as well as straight. Another option to consider is to get a cutter designed specifically for porcelain tile.
Practice before you begin making cuts on tile you want to install. Cutting ceramic tile requires a degree of skill, so even a little practice will reduce the number of chipped tiles you end up with. You can keep the cost of practice down by asking your tile dealer for some scrap or surplus tile to practice on.
Measure the space where the tile is to be placed carefully, and mark the cut line with a carpenter's pencil. Accuracy is important here. The more carefully you measure, the fewer tiles will have to be recut. The fewer cuts you must make, the fewer chipped tiles you are likely to have.
Place the tile on the tile cutter with the marked cut line aligned with the cutting wheel. Pull (or push, depending on the tile cutter design) the scoring lever in a smooth motion until the surface of the tile is scored completely across.
Press down on the lever. This applies an equal pressure on each side of the scoring in the tile, snapping it in two along the scored line.
For large projects or ones with a large number of circular or other odd-shaped cuts, consider renting a ceramic saw from your building supply dealer. A ceramic saw is a power saw with a water-cooled cutting edge.