For whatever reason, all the crap that can get me down in my personal life has never been able to infiltrate my professional world. When it's interview time, here's my secret:
"I am interviewing for my job."
I convince myself that it's already my job. From the very beginning, when I find the job that I want, in all of my communication with that employer, I tell myself in my head that it's already my job and I just need to remind them about that little oversight.