One very nice thing to do to your regular G chord in first possion is to move your pinky over to the second string third fret   this gets rid of the B third in the chord.and makes a D note ( stay away from the first string though unless you want a seveth note adding idex finger at the first string first fret to be bluesy) )... . THis makes a very churchy round G chord . ADD a C chord onto this with out moving the Pinke and you get a great transitional chord . Also when doing your normal D chord add the thumb at the second fret sixth string to add a round third . All transform those chords .Together they make a very romantic sound . Also add a C note to the G chord to make a G sus 4 (use your index finger for this) . THis is the chord at the beging of A Hard Days Night but is also one of the oldest folk layerings : (to add a sub domiant note to the tonic) . Have fun , All the best , Guy