Explain what you re trying to do. Even though no one is a certified representative of their own ethnic group, they can let you know when something you propose is totally out of whack. And they can point you to sources of specific info. If you re thinking of approaching someone who s more an acquaintance than a friend, offer to buy them lunch, or dinner, and make the interaction a formal interview. This is what you d do with anyone else you wanted to pump for valuable data.
Cultural background is data.
Above all, don t rely on representations of minorities gleaned from popular culture. A lot depends on your piece s point of view, and the size of a given character s role within it. By rights he belonged in a red blanket, skin gleaming with oil, hair plaited. Instead he wore the tan shirt, pants, and zip-up jacket of an engineer from Buildings and Grounds, and his hair was a modest Afro, as they called it, around his narrow face. Here we see the minority through the eyes of another minority, but one sharing many assumptions with this society s rulers.