Google "Photographing Artwork" (or something similar) and you'll find numerous entries online with tips and instructions on the how to capture the best image of your piece.

Here are few links that we've found which might help:

First, watch this brief video

Some other sites with easy and effective "how to" instructions:

How To Photograph Your Art the Easy Way!

How to Photograph your Artwork for a Portfolio or the Internet
(be sure to check out the additional links at the bottom of this page)

SECRET TIP:
All of these sites recommend using a tripod, if you haven't got one,
try this:

The Secret Camera Tripod In Every House