Take care to make sure none gets on the wheels. Older tires are very brittle, will slip, and will break if you attempt to remove them. Replacement tires and the tool to install them are available from hobby shops, but if the tires look healthy, don't try to replace them just yet. If applicable, clean the wheels on the tender and make sure both trucks are making good electrical contact with electrical pickups. Do not lubricate axles where they make contact with pickups.
Reassemble steam locomotives.
Where rods and steam gear actuate in slides attached to the body, apply a drop of lubricant on each set of slides once assembled. Do not force rods or spin wheels to get things lined up during reassembly. Also, reconnect the tender to a steam locomotive if it is part of the electrical pickup circuit. Make a cradle that stays free of the wheels of the locomotive when the locomotive is on its back. For steam locomotives, it should also support the tender but not foul the rods and slides on the sides of the locomotive.