i think a good way is to play by ear. if you know the song by heart, and in your mind you can listen to it with all it's instruments, then while you're playing with just the chord charts or something, you can start just figuring out what goes where to add bass/keys/rhythm/lead/harmonies on the guitar while you sing. of course it's not like you can ACTUALLY play all or even a few of the parts in their whole, it's more like... you just got the main riff, or the chords, then you sort of compromise, usually keep the root note their and maybe part of the chord while you use your pinky to play out a melody or something while you sing, stuff like that.
since you're just starting out, i'd advise getting your chops good. like being able to switch all sorts of chords, play melodies over chords, stuff like that.