how to deal with interview jitters......

So how does everyone else prepare themselves for a job interview? I have one tomorrow and i can feel it already starting to get to me, kind of like a huge knot twisting in my stomach........i just don't think i've had much experience, i had my first one ever only a few weeks ago which was good practice i suppose, and i got the job, but i was an internal candidate and had already been there 6 months so i think it's a bit different........i was still nervous as hell, couldn't get any sleep the night before etc.........i say to myself all i can do is just run over what they're gonna ask etc and give it my best but it's still not very reassuring, i think i'm shitting myself because this could be my big break, the job involves working for a consultancy firm on the stock exchange, so you can imagine i feel a bit out of my depth........i had the first stage HR telephone interview last week where they ask you about your strengths and weaknesses, scenario based questions etc and i must have done alright because they've called me back for a final interview on my technical skills.......i'm not the kind of person who'll bottle it and not go but any tips would be welcome, think i'm gonna go for a swim to get my mind off it for now but i'm not looking forward to trying to get to sleep tonight, luckily interview's in the afternoon so hopefully i won't be feeling too rough........how does everyone else cope?