Many small toys and collectibles, in particular trains, rely on small electric motors for their motive power. Keeping these engines in good working order is an essential part of protecting your investment. Proper and regular maintenance, including oiling, is your first line of defense.
Unplug the motor, or otherwise disconnect it from other power sources, such as batteries.
Clean the motor and the area around it. Vacuum up any debris or dust on, or in, the vicinity of the motor. Dip a Q-tip or cotton swab into a small amount of rubbing alcohol, and wipe around the edges of the motor, paying particular attention to the drive shaft. Use small amounts of alcohol on the swab, and continue to change swabs until the swab comes away clean, with no dirt or grease.
Drop a small amount of oil at the drive shaft junction, where the shaft goes into the motor. Some motors may have a reservoir for lubrication, opened by removing a screw. This is quite rare with small motors such as found in toys. Consult the manual if you are uncertain about any lubrication points.
Wipe any excess oil up with your clean rag. Reconnect to power source, and test to be sure the motor is operating properly.