Had a bunch of them for sales-oriented jobs in the past (recruitment jobs, to be exact).
You need to find a balance between the shy, nervous-wrecks who, when called-up to speak, can't deliver more than 4 words without giggling like a punk, and the OVER-THE-TOP c*nts who break out the jazz hands after telling people why they love people, even the people they've just met type of people.
Just be yourself, but always maintain your composure, be outspoken, but not to the point that you're OVERLY dominating the convo and be clear and concise with your answers.
They're not difficult, just a way for the employer to weed the flakes from the 'bout it, 'bout its.