If it's a basic ceramic tile and a straight cut you can use a simple board cutter. These can be obtained for a reasonable amount of money at most home improvement stores. If it is more complicated or a natural material such as stone then you should use a wet saw. Unless this is your trade you will probably not have one of these laying around either however, they are available for rental and will provide you with the cleanest cuts. If you have a small job that only requires a few cuts then you can use a grinder with a diamond blade that can again be purchased at a nominal fee.
A tile wet saw with a diamond blade is the easiest, even with the cheap bisque tile. Machines are usually common at tool rental outfits. Finally, they are so safe to use! You can hold your finger against the blade and it won't cut it. However, hold it there long enough and you will get a burn. Be sure water is flowing directly over the blade or risk burning out the diamond blade, not cheap to replace!