Give yourself a half and hour buffer to make sure you get there on time, can park, find a restroom, check yourself out in mirror, do some touching up, breathing, calming, orienting.

Arrive at the office itself approximately 5 minutes before your interview. No sooner than 10 minutes before, no later than 3 minutes before.

Use a different type of paper for your resume (I like heavy weight gloss/matte), and bring at least two copies, ideally three (one for yourself, one for the interviewer, one if there's someone else). Bring your references on the same paper, bring your cover letter on the same paper, bring the research you've done on the interviewer/company, on the same paper, bring the questions to ask, on the same paper, and so forth. Stacked up nicely in a folder. Paper clips, not staples.

This may not work for other people, but what works for me is: I imagine I'm seducing someone. Reason this works for me is because I believe in long, slow, gradual seductions, very subtle. Helps me get into the right mindset. I'm not sexually objectifying the person, it's more a mindset that helps me get in the right role.

Do research about the company or person who is interviewing you. Remember facts about it. Come up with questions. Come up with ideas. Be prepared to discuss intelligently.

No chewing gum, fussing with your hair, squirming in your seat, slouching, grabbing your crotch, adjusting your bra strap, burping, tapping on the table, etc... sit comfortably up right, paying attention to the interviewer. Don't lean toward them overtly, but don't retreat either. Firm handshaie, not too weak, not too strong. Look them in the eyes, smile, and say, "good to meet you in person" when you do.

Never cut your hair, wear shoes/clothes you've never worn before, use a bag you've never used before, color your hair the day before your interview. If you're gonna do these things, do them at least 2-3 days before the interview.

Practice, practice, practice. Film yourself, have someone ask questions, so you know what you look like, what you need to work on. Rehearse common interview questions and your answers over and over and over. Simple google search will tell you what those common questions are.

"What's your biggest weakness?" What they're looking for is how you approach challenges, and it's a personality thing as well, testing your self awareness et al. Maybe you're hyper detailed, and in times past had problems (not too horrible, even if it was, mention casually, lessen the impact), but this is how you fixed it. The general line of thinking: challenge, learning, result.

Another general rule: yes/no conversations are boring. Ask them questions. If you answer a question or say something, be prepared to back that up with an example. Interviewers like concrete examples rather than empty filler.