If your guitar has the closed back type (ie: Martins, Grovers, Shallers, etc.) no maintainance is required since they are self lubricating.
If these tuners become loose or slack, and you notice this when tuning your strings, tighten the screw in the side of the part your finger grips, just enough to remove the slack. The gears should have a nice easy feel when tuning, but without any slack or waggle to them. You might want to play around with the screw adjustment to get it just right.
If on the other hand you have open, or "butterbean" tuners (ie: Waverly, Martin, or classical style tuning gears) 1 drop of sowing machine oil per gear once a year, is all it takes to keep them in good shape for many years to come.
Anyone want to add anything about gear ratios?
One other thing, and to clarify for novices, the areas that are actually (and generally) adjusted during a "setup" are the saddle (white piece of plastic or bone, that the strings cross over on the bridge) and, the nut, (white piece of plastic, micarta or bone that is just above the first fret on your guitar.)
For more corrective measures that the above setup might not entirely alieviate, a "fret dressing" (planing, smoothing, leveling and filing down of the frets) can help a lot, and make the neck feel even more comfortable, as your fingers won't be as inclined to "catch" the frets when sliding up and down the fingerboard.