I can't understand why this thread hasn't reached the hundreds.
Anyway, here are a few things I find useful:
   
   Remember the other hand is as important as the fretting hand: play ant tabs you can to be able to instantly pla the string you want.

If you can read music or know someone, piano music often gives more
intertesting chords and indeed bass notes against the chords.

The most rewarding thing is to listen really carefully to a cd and work things out. This is hard if you don't give yourself a chance by finding out:
Is it in standard tuning?
Is it capoed?
What instrument type?

    Here you want to look at videos, TV etc and also listen for what strings ring out as open strings.

    The biggest thing, in my opinion, is to love a guitar part so much that you simply have to learn it; this builds technique.
Those who want to play purely as accompaniment, the singing being more important to them tha guitar technique, are unlikely to be able to put in the hours. An example would be "Fire and Rain" - do you want to play it as recorded, or just "well enough", because the tab is readily available for many classics.

   Some simple theory is helpful too. Know the intervals of the major scale and learn diatonic chords. Chord spelling is very useful, also.

    Finally, there are some great players who don't think much about what they are doing, but they are just lucky in having the ears.
One last idea: learn to strum lightly but with decent volume and , when
fingerpicking, use the thumb as the basis for the rest.

    No doubt there will many different views, but remember it's meant to be fun, although the better you get the more fun it is!