Fine tuning your locomotive?

How exactly do you fine tune your locomotive? I hear this term used all the time and really don’t know much about it. Can someone help?

When I tune locomotives heres some of the stuff I do:
Check all drive train parts to ensure things are shaped correctly and are free of flash.
Worm gears, bearings, regular gears, axels.
I make sure all the valve gear flows smoothly without any binds. Which means I disengage the worm gear at the top of the tower, and slowly roll the mechanism on a piece of glass.
Check the springs on the pilot and trailing truck for optimum sprungness. If its too stiff, i’ll cut a few prongs off.
On an articulated, I make sure both engines pivit well and don’t rock side to side too much.
Every moving part–motor bearings, gears, drive coupling joints, every rod connection, wheel axels–gets some lube.
Then I clean all electical wipers and wheels with alcohol soaked q-tips.
And I run it at low speed. Forward for a few mintues, then reverse for a few miniutes.

What brand of locomotive are you wanting to fine tune? Each brand of locomotive differs in fine tuning even though all brands share the basic drive design.