I think it's a start, but i also think there's a way to go. What was your lighting set-up?
#1 Seems like a very awkward composition to me, but the lighting and exposure are acceptable, other than a minor glare on the chair back. I think a 1/3 - 1/2 stop brightening would help.
#2 has the best overall-exposure, but the guitar appears soft; it looks like the point of focus was the seam on the chair's back-rest. There's a little hot spill on to the background, and I don't understand the crop, but lighting is good here.
#3 has a lot of spill on to the background (A quick run-over with a hot iron will make a world of difference to those wrinkles) and an unfortunate glare on the upper, LH portion of the guitar body; this looks to me like lack of diffusion.
#4. Way, way, way under-exposed.
What sort of modifiers were you using? It looks to me as if you needed more diffusion material between light and subject, but they're definitely a good start.
Just my $00.02 worth - you mileage may vary.
~John