For G, I like pinky on first (highest) string, fret 3; middle finger on sixth string, also fret 3; first on fifth string, fret 2. That leaves ring finger free to either fret the second string at fret 3, to leave the B note sounding only in the bass and getting a more "droney" sound (bluegrassers call that the "Tony Rice G), or fret the fourth string at fret 3, producing a G7 with the seventh in the bass, which is a nice passing chord going to C.