Start by picking a string gauge you like to use as a rule (light or medium). The SCGC strings are good place to start because you know SCGC guitars are meant to sound good with them.
As you bought used, I would suggest taking the guitar in to a luthier/repair person who does acoustics well. Have him or her look at it carefully and do a set up. All guitars need set-ups from time to time. Consult with SCGC for the nearest suggested luthier.
Never fear the sound is in there, it just may need some TLC to come out.