I'm not an expert, but from trial-and-error while doing this kind of thing recently I'd suggest the following:
Put the photo on some kind of stand/easel, and use the best camera you can, mounted on a tripod.
If possible, get the camera to put gridlines on its screen/viewfinder, to help you get the alignment right and avoid skewing it. (However, some programs have tools or plug-ins for correcting skews, so this can be adjusted later if necessary.) Zooming the lens in or out is OK, so long as you don't go into the digital zoom range.
Use the highest resolution available, and allow some margin round the outside of the photo/frame - you can crop some off later, but you can't add in anything that the camera missed.
Don't use flash, and if the camera is up to it, use natural light only. However, any light coming from behind the camera will create a reflection, so make sure you have your back to a wall or a thick curtain. Overcast but brightish conditions are best, as the light is diffused, more constant and less directional than strong sunlight.
If you do use artificial light, again make sure that it comes from the side (preferably some from each side), and adjust the white balance as appropriate.
If your camera has it, use a delayed shutter setting to avoid any shake - this can occur even on a tripod.
Be prepared to take a number of shots with different settings - this may depend on what the camera is capable of, but try Auto and Manual as a minimum.
As an alternative to the easel/tripod set-up, I've had fairly good results by putting the picture flat on the floor next to a french door (out of direct sun), and putting the camera on a tripod with the head turned to point straight down. However, it's a bit tricky getting the right position as the tripod legs tend to get in the way - I found it best to have the tripod at maximum height and then zoom in.
As I said, I'm not an expert, and others may have other ideas, but this is what's worked reasonably well for me.
Arthur
