OK... it's all about the lighting.
A guitar is a good subject for shooting as an exercise for a number of reasons:
1. Guitars are cool. I know, I know... most will tell you it's the drummer that gets the women, but really... everyone KNOWS it's the guitar guy.
2. Guitar bodies, pickguards and head stock have interesting curves. These factors along with the length of the guitar offer a vast choice of angles for both over-all and detail shots.
3. The strings, frets and tuning machines offer repeating forms that converge as the distance from the camera increases.
4. Highly polished surfaces of the body and pickguard.
5. Detail in the knurling of the knobs, pick-ups and bridge... even the wound strings.
6. Reflective metal surfaces of the tail piece, jack and tuning machines.
These are some of the things you can approach in making your photos.
I suggest you start by addressing over-all lighting. Since most of the subject is glossy, I suggest you take it to a large window at a time when the light is bright but not direct. If there are white sheers hanging, you can close them to diffuse the light. The larger the window the better, but make sure the sun is not falling directly on the guitar. Then, directly in front of the window, hang a white bed sheet... maybe 6 feet or so away from the window. Nothing fancy. Maybe you can drape it over a couple of stools or, even better, some sort of rod supported by a couple of stools.
So we have the window, then the guitar (either on the floor or a short support) and finally the sheet. Now you're ready to take the camera and do some exploring. Look through the lens at varying zoom levels. Move around the guitar. Move the camera up and down. Once you settle on a couple of different view, put the camera on a tripod and move it into position. Before moving on to the next view, upload the image to your computer and review it, leaving the tripod in place. If you see some things you want to adjust, return the camera to the tripod and make any adjustments. Once you're happy with that view, move on to the next.
I hope this helps.
-Pete