This is Your Mother speaking.
Bathe.
Brush your teeth. Check them in the car mirror before you go in, for spinach and other dangly bits.
Look nice.
Wear a suit.
With a tie.
Leave the lapel pins at home, don’t care whether it’s Jesus or AIDS or an American flag. Leave it off.
Extremely muted cologne, if any.
Remove the piercings.
Watch the liquids–don’t tank up on multiple coffees or Pepsi beforehand out of nervousness, because then of course you’ll have to pee like billy-o during the interview, which affects your concentration.
Be on time.
This means you figure out where you’re going to park your car ahead of time. Allow extra time to circle the block. And take extra quarters for any potential parking meters.
It’s better to get there an hour early and have to sit there in the waiting room than to be late because you couldn’t find a parking space. Plus, sometimes if you get there way early, good things happen, like, “Oh, since you’re here, why don’t you come sit in on this meeting, see what you think about the way we do things.” Then you’ve got a leg up on all the other candidates, because the Boss gets to see how you actually interact in their work environment. At the very least, you’ll get a rep as an eager beaver who doesn’t mind sitting in a waiting room for an hour.
Bring something small and old-fashioned to make notes on, like a small memo book and a couple of pens (that work) or pencils. This makes you look organized, and not as trendy or pretentious as whipping out a handheld to make notes on.
Shut off your cell phone for the duration of the actual interview. And I mean “off”, as in “hold my calls”, not “off” as in, “Vibrate”.
Don’t ask how much the job pays right off the bat. Let them tell you.
Don’t ask about vacation time, ditto.
If the interviewer is female, for god’s sake don’t look at her breasts. Keep your eyes firmly focused on her face at all times.
Don’t hit on the receptionist/secretary. If you do get hired, she has the power to make or break you–formidable ally, equally formidable enemy. Be very polite to her. And don’t check out her breasts, either.
Don’t forget your resume. Carry it in a (new) 9 x 12 envelope (or a briefcase, of course, if you own one), so it looks good and if you drop it, it doesn’t get all dirty and flutters all over the floor. Have a copy that the interviewer can keep–don’t cluelessly say, “Oops, that’s my only copy, could you make a xerox…”