Well the photographers job is to get the best out of you, so let him worry about your pose. However, relax, be natural, shoulders back, elongate your neck, chin slightly up to avoid double chin. Don't wear too much foundation that will sink in to creases or heavy black kohl that may age you. However do wear a bit of bronzer as flash photography can make you look pale. And blot blot blot before you go in so you don't look greasy and shiny.
Clothing wise, something smart and neutral without spots or stripes as the camera can distort these. Make sure no bra straps are showing or the shirt is straining across the bust. No sweat marks either.