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?)
![Grin ;D](https://www.carls-sims-4-guide.com/forum/Smileys/default/grin.gif)
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.