To expand ever so slightly on Kevin's advice. For pwts three or four photos are desirable - (1) straight on from the top, (2) a side shot to give an idea of the proportions of height to diameter, (3) A clear shot of the base, and (4) a clear shot of the signature or marking if possible.
For other glass (1) a general shot as you would look at it, (2) a side one shot for proportions, (3) a clear shot of the base, (4) a clear shot of the rim at the top, and of course (5) a clear shot of the signature or marking if possible.
Shots should be taken against a plain background - usually white is best. In the case of signatures try to arrange the photo so the patterns in the glass are not present, and the markings are easy to read. Hope this helps.