Rear derailleurs for the most part are relatively maintenance free except for lubing and cleaning regularly. One minor fix you may have to perform on a regular basis is an adjustment for when the chain becomes loose or performance is affected. This tutorial will give you the step by step process for a Shimano rear derailleur adjustment.
The parts that need to be adjusted are the upper limit, lower limit, cable tension, barrel and b-tension. The first thing that needs to be done is to pedal so that the rear derailleur fits into the small cog. Then tighten the barrel adjuster all the way in so there's adequate room for adjustment. For a starting point we'll adjust the upper limit. Turning the screw in moves the Shimano derailleur inwards whereas spinning the screw out moves the piece in the opposite adjustment. The ideal location is a position that puts the upper pulley right underneath the small cog and just barely outboard.
Loosen the cable anchor and pull the cable tight before tightening the anchor back in. With the bike upside down you should turn the pedals and go through the shifting cycle. If the shifting is sticky or off balance you'll need to tighten up the barrel adjuster to make each gear hit cleanly. You'll need to play around a little bit to fine tune where the pulley lines up.
To adjust the lower limit shift the derailleur into the largest pod. There's a small screw that needs to be adjusted so that it's impossible for the Shimano derailleur to overshift into the spokes. If the chain clicks when shifting in and out the screw needs to be adjusted out so that it goes in cleanly. The last step in adjusting the rear derailleur is to adjust the B-tension screw which changes the angle that the unit sits on. You want the piece to be as close as possible to the cassette so that the derailleur shifts quicker and the chain lasts longer.
Something you need to remember when adjusting a Shimano rear road derailleur is that it's largely a trial and error process. You'll need to establish starting points for the location and tweak them intermittently to get the most efficient shifting possible.