Chose simple matboard colors. Animation art is typically very colorful, so pick white as the outer mat. Find a color that matches the art for the middle and use black as the bottom mat. If you are framing an expensive cel, you can use a white or cream linen mat with a gold or colored fillet. This will add richness to the display.
Pick either black or gold frames. Because most characters are outlined in black, framing your cel in a black Formica frame allows the cel to stand out, and not the frame. With cels that you are framing with linen and fillets, a slightly ornate gold frame will add a vintage look to the cel.
Use acid free materials. Whether you have chosen to frame your cel yourself or if you use a framer, be sure all materials including tape and matboards are completely acid free.
Frame with UV Plexiglas. UV (ultraviolet) Plexiglas is the best way to preserve your art. The ultraviolet will protect from fading and the Plexiglas will save your art from ripping or tearing should it fall off your wall.