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stored Running Trains that have been Stored
step 1) Visual Inspection
A) Look for dirt, dust, loose wheels, hair and fiber around the wheels and axle.  Make sure all wheels are clean, especially the metal ones used to supply electricity to the train. Gently wipe (or scrap sometimes) the dirt and crud that tends to collect on the wheels.
B) Make sure all mechanisms are operating smoothly. Rotate motor with finger.  Never apply power to a motor unless the armature spins freely.
C) Check the wires to the plug in the panel in back of the cab.  One or more may be broken.  To reconnect, pull out the plug.  Heat the pin to which the broken wire goes with a soldering gun and then sitck a piece of thin wire into the tiny hole in the tip of the pin to drive the broken wire remains out of the pin.  Then reconnect the wire.  You may have to add a short piece of wire. wire diagram
D) (optional) Carefully check the brushes to make sure they are contacting the comutator face.

step 2) Lubrication (use a ‘plastic friendly’ lubricant like Labelle http://all-railroads.com/lablubes.htm) click here for details
Per AC Gilbert :

step 3) Reverse Unit  Most locos have a reverse unit in the tender.  Take the shell off the tender and spray a little tv tuner contact cleaner on the drum and fingers.  Often power does not get to the motor because the contacts are not contacting the drum due to dirt and corrosion.  TV tuner contact cleaner is sold at Radio Shack and lots of other places.  It comes in a spray can with a little red plastic tube that you stick into the button to aim cleaner at precise spots.  If the drum of the reverse unit is very dirty, you may want to clean it.  To do this, unscrew the screws holding the reverse unit to the tender floor, turn the reverse unit upside down, and clean the drum with q-tips and contac t cleaner. click to see more

step 3) Test Run
A) Never apply power to a questionable motor for more than a few seconds at a time.
B) Always test locomotive by itself without other cars attached.
C) Use minimum voltage (8-10 volts)

(Thanks to Tom Jarcho and others for help with this page.)