When I interviewed for my job I went into the interviews I convinced myself I didn't want the job so that I wouldn't feel as nervures but still give the best possible interview I could. Don't be over confident but make sure you self yourself as a confident programmer and peerson in general.
I interviewd for a position about 6 months ago and they said they love me as a person and what i could do but I didn't praise the company enough, so make sure you do your research on the company and ask questions about things like staff turn-around, staff development schemes, technologies you'll be using (other then C# .NET) and are there any plans to move into different technologies in the future.
Luckily enough for me, not getting the job mentioned above meant I was able to interview for my current position which is exactly what I was looking for and I'm lucky enough to be working with a really good development team.