DIY Guitar Care and Repair

Have you learned to do some common guitar repairs and adjustments yourself?  Do you change your own strings, or do you prefer to have a professional take care of it?  Have you ever adjusted the action or installed a tap plate or pick guard on a guitar?  

If someone is new to the guitar and generally handy with  hat sorts of minor repairs are worth learning to do yourself?   What things might seem complicated, but are actually pretty easy?  What sorts of repairs and adjustments are better left to a professional?  

One of my early guitar adjustments was adjusting the height of the saddle to lower the action on my nylon string guitar.  At first I sanded it down too much and thought I'd made a horrible mistake.  Fortunately, a thin strip of balsa wood was enough to raise it to a playable, flamenco-appropriate action.  Ten years later I've never needed to make another adjustment.  Also, getting a new saddle for a guitar is just not too expensive, so even the worst-case scenario is not a disaster.  

One common DIY project that I've seen less success with is installing a golpeador or tap plate.  the equivalent of a pick guard for flamenco guitar, to protect from all the tapping and percussive strumming we do with our nails .  Most flamenco guitars come with the tap plate installed, but some guitarists think to install one only after they have been tapping quite a bit on their guitar.  Once the finish and/or wood has some dents in it, it's more difficult to stick on a tap plate smoothly, and they can tend to bubble or peel.  

What sorts of routines do you have to keep your guitar looking nice and playing comfortably?  How do you take care of the finish?  Any products you recommend?