You need more notes!
Assuming a key of G and not some funky mode, you are playing 1,5,4, and 2. (G, D, C, A) 2 isn't going to do much for you. I would suggest going with a 6 and a 3 and expanding your box to include the d string and the octave G.
G------------------------------------
D-------------5----------------------
A-------3-----5-----7------------------
E-------3-----5-----7-------------------
Making your first position on the 5th fret rather than the 3rd will change the tonality. I would stay away from the C unless the chord you are playing under is the subdominant.