If you want to be an impressionist, or at least impress your family at Thanksgiving, you should learn how to do a William Shatner impersonation. Even William Shatner occasionally does a William Shatner impersonation, overemphasizing his distinctive voice and speech pattern that has helped the routines of stand up comedians and stage impersonations for decades.
Widen your eyes and inhale audibly with your mouth open.
Raise both hands and karate-chop them up and down with nearly every word you speak, even before you speak.
Say the first word of the sentence.
Pause, frown and mostly shut one eye closed. Point at the audience, wagging the finger ever so slightly.
Say the rest of the sentence as fast as you can and then the first half of the second sentence, going from pointing to karate-chopping again.
Pause, look around without moving your head and repeat as long as necessary.
It's more important to talk like William Shatner than to have your voice sound like Shatner for people to immediately recognize who you are impersonating. Most audiences associate Shatner with Captain Kirk, but if you know your audience likes "Boston Legal" and not "Start Trek," act more like Denny. Perform this in front of a mirror to get the facial expression down pat. You can also record your impersonation and play it back to hear how you can improve.
Don't do a carbon copy of stand up comedian Kevin Pollak's impersonation, who is considered Shatner's best impersonator. Put your own little stamp on the impersonation, such as sticking Captain Kirk in a very modern situation.