Start by perfecting the celebrity's voice. Most audiences will forgive an imperfect look as long as your vocal performance is easily recognizable. Impersonate someone who speaks in a vocal range that's easy for you to reach. Men might find it simple to mimic John Wayne or Jack Nicholson, while women can imitate Lucille Ball or Joan Rivers.
Perfect the celebrity's trademark lines that audiences will identify immediately. Try one of his famous quotes, a classic line from a movie or television episode or a flub from a television interview, for example.
Mimic the person's mannerisms. Watch one of her movies repeatedly or study her behavior during interviews to discover how she holds her hands and gestures as she speaks, the way she tilts her head and crinkles her eyes when she smiles or how she fiddles with her hair or jewelry.
Adopt one of the characteristics of the celebrity's physical appearance. Quickly give yourself Christopher Walken's spiked hairstyle or put on a pair of dark sunglasses like Jack Nicholson, for instance. In addition to hair and accessories, observe the person for trademark clothing or makeup styles.