If you would like to take a picture where the stitching pattern shows up (many longarmers photograph their work specifically for this) then sidelighting is the way to go. You want a distinct source of light, such as near a window or sliding glass door on a bright-cloudy day or one that faces north (in northern hemisphere) on a sunny day.
To show the piecework or applique you want a broad, diffuse light source such as outdoors on a bright-cloudy day.