Hmm, funny that you posted the same pic 8 times, hehe. N00BZY ALERT!
. . . Just messing with you
Why C64 palette? Why not a custom palette? Your C64 palette is 16, not 12 colors, btw. I highly recommend a basic ramp for your palette, since you're n00b level runs high at this time. The C64 palette is rather unforgiving.
Are you really posting this here for help before you've even tried yourself? I see no attempt to shade this guy in yet.
Get reference from the web. Pull off yer shirt (woo) and stand in front of the mirror. Observe. Where do the main patches of light and shadow fall? Now go and paint up Rufus here with that knowledge.
Let's not even bother with the anatomy issues . . . hmmm . . anatomy . . . I seem to remember founding some fake anatomy guild once . . . where was that . ? .
But, anyway, give this your best shot, THEN post.