Clean up the background.
I bought some black felt at a fabric store for a couple dollars a linear yard. The stuff I got is 72" wide (6 feet) and I bought about 5 yards.
I tacked that to the drywall in my garage and the only light I used was one of those 500w construction lamps placed off to the left.
I angle the guitar(s) to the right until I have the shot I want WITHOUT reflections.
Use a tripod! Even with a fast shutter speed there is enough movement with a handheld cam that you ever so slightly blur the photo.
Also, use the shot timer, mine is variable, I set it for about 4 seconds. Anything will do as long as you can get your hands off.
Don't use flash.
Get the camera to the height of the guitar, stay back about 10 feet and use OPTICAL zoom (never digital zoom) to fill your frame. If you get too close to your subject the proportions get out of whack.
These are my results:
In that last one of the GS-Mini back I had the light angle wrong and was picking up glare, I tried to kill it by holding a sheet of typing paper in front of the lamp but some glare still came through.
This is the lamp style I used for all of these:
I removed the wire cage from the front of the lamp as not to cast shadows. Keep away, it gets HOT!
All of those were shot with only that lamp, in the closed garage that was otherwise pitch dark.
-K