Hell yeah wear a tie. People judge you in the first 20 seconds........so go in and make an impression. Take time to think about the answers to questions........and listen to what they are saying and try to respond intelligently. If you cant do that, keep quiet. Keep polite and dont let them lull you into a false sense of security.
know a lot about the company and position. ask a lot of questions. confident, not cocky. look interview dude in the eye but don't stare him down like you wanna beat his ass. Dress proffessional, but don't outshine the atmosphere...send a letter a few days later thanking him/her for their time.
yeah, dont show up looking like casper he fucking ghost, and dont have your nails looking like you have been scratching a homeless man's ass prior to the interview.