I would have a magazine or portrait of that particular person you are trying to create. Also, there is more than one skin color, besides the brown, you could either do the yellowish-tan or the rosy pink too. If the celebrity you're creating has been in the spotlight in a crazy way, give them a special athletic outfit. For Charlie Sheen, I either give him a pirate outfit, or a ninja one.
Sliders are great too! They can really give you an accurate stance. Body hair can work too. It makes them even more accurate. (David Hasselhoff anyone?)
Most importantly, don't use any sort of realistic skin tones, or "anti pudding" mods. It appears to be trying to hard, and it looks very creepy. A good Sim representation of a famous celebrity, still has the Sim look. The way Sims are suppose to look. Plus, you don't want to infect another person's game with a virus do you? Especially those who don't like CC.