Portfolio!!

Hi there!

I am trying to put together a portfolio of my work so i can use it in job interviews. Which is the best to go? for a studio look with clean white background or outside, being more urban? i want it to look as professional as possible but need an idea of where to start! how many images are a good idea? I've never seen another portfolio so i'm not sure what standard to set it to. I'm sure i'm over thinking this but really want it to be good! Any ideas or advice would be very much appreciated!

Many thanks.