There are many simple ways to do this. One of the best ways is just to go to any convenience store or dollar store and there they sell special coloring that is easy to use. All you have to do is apply to any tooth or teeth and you can enjoy your golden teeth ;)
If you're wanting to make some fake gold teeth for a child, the easiest thing to do is get some gold foil. You can find this on certain candy bars and even bubble gum. Take the wrapper and mold it around the tooth or teeth that you're wanting to cover.