I haven't interviewed in a while but here's some advice.

Study the materials they outlined for you in the interview email.
Know the systems of your current aircraft in and out and be able to draw them.
If you're not instrument proficient, get proficient in a Frasca Sim.
Be humble, ask questions, be courteous to everyone you meet, including other interviewees.
Lastly, pick the honey baked ham for your lunch choice. Oh, and no matter what DO NOT take off your suit jacket, even if asked to do so.

Good luck!