For the benefit of someone who hasn't worn a suit very often, there are a few "rules":
When you buy the suit, it will have some tags sewn on to the sleeve that should be removed. If you havent purchased a suit (or if it's been a while), you should be measured at the place.
If wearing a colored dress shirt, it shouldn't overpower the suit.
Buttoning the Jacket: When standing up, your jacket should be buttoned; when sitting, unbuttoned.
Most common jacket is a 3 button jacket. When buttoned, the top (and middle button sometimes) should be buttoned, but not the bottom button. I've also heard that some button the middle only. Just don't button the bottom one, it's not really meant to be buttoned.
For a jacket with 2 buttons, just the top one buttoned.
Socks are usually a darker shade of the pant color.
And don't wear cologne to the interview.