i work in the jewelry industry so my opinion is based half in photography and half in the world of jewelry and jewelry advertising.
Generally you won't see a watch on its side in an image. There are several positions that are common, and quite flattering to watches. Remember, the face is the key.
1. Straight up and down with the face fully facing the camera
2. Straight up and down with the face slightly tilted away from the camera. This shows off the band a little bit as well.
3. The face of the watch is facing the camera directly, but the whole watch is tilted several degrees so that its off kilter a bit.
With regards to background and jewelry shots, you'll want to almost always go with a white background. The other part of jewelry photography that can be incredibly difficult is reducing the glare and blown highlights that can come from objects that have so many angled surfaces and reflective parts. Jewelry photography can be TOUGH to get right. Even in advertisements in my own industry, we see failures all the time. Don't be surprised if it takes you a while to capture an image that truly captures the design and beauty of the watch or jewelry you're shooting.