Don't put on too much cologne. Wear a suit. Bring your resume(s) in a folder. Have a pen in your pocket. Leave everything else (jackets, backpacks, umbrellas, etc.) at home. It can take you several minutes to put all that junk down and settle in - not a good impression. Arrive 15 minutes early. Be extremely polite to everyone in the office, including the interns and the secretaries (who might put in a bad word for you if you piss them off). If they offer you coffee/tea etc., say "No thanks, I'm eager to get started." After that, it's all up to you.