If Silver is your number 1 choice, and you have time, I suggest you interview somewhere else first to get the experience.

I don't know the 40 question test but typically its pulled straight from the ATP question bank, mostly weather and regs.

Wear a suit & tie and black shoes. Firm handshake, look your interviewer in the eye and smile. If you really want to impress, bring a brief case with all your paperwork neatly organized with copies of your resume, medical, passport, fcc license, pilot certificates etc.
The general rule of thumb in an interview is to remain positive at all times. You don't hate flight instructing, you just feel its time to move on to the next stage in your career.
You get the idea. Good luck.