I agree with Peter about using continuous lighting. Flash can be very frustrating if you're not used to working with it.
Two things... when photographing artwork you need to be sure your camera is perpendicular to what you're shooting. Otherwise you can end up with parts of the image that, depending on the aperture you use, can be slightly out of focus. Professionals use copy stands that are made for this exact purpose. However, you can get by with mounting your image on a wall and shooting from a tripod. The important thing is to make sure that your camera is level.
Second, you need a flat, shadowless light source... or sources. I would recommend a ring light to go with the macro lens that Peter suggested. LED ring lights can be purchased that feature both continuous and flash settings. Most of them also have diffusers that snap on the front of the LED panel to create a softer, more flattering light.
Then you need to experiment to find the camera and light settings that produce your desired effect. Trial and error.
--Ron