I typically get job offers from almost all of my in-person interviews. What works for me is being very engaging in the interview. Appear genuinely interested in the company. Don't wait for the "do you have any questions for us" part of the interview before asking questions, ask questions throughout the entire interview. Ask questions about the corporate culture, ask questions about their internal workflow, ask questions about parts of the company other than the one you'll be working in.
Also, come off as very human during the interview, especially when they ask you about yourself. When they ask you about yourself, don't just rehash your resume, they can read that for themselves. Instead, talk about your interests, your hobbies, your life. "Well, I've been a programmer for 13 years, I have a BS in computer science from the U of M, I've been married for 3 years, I play softball and pain miniatures."
The interview is way less about them gauging your technical ability, and way more about showing your interest in the company and how you will fit in with their current team.
Yes, be prepared for the technical questions too, but that's really the minor stuff