I feel like this is particularly heightened for an NQT as you're jumping into what seems like unknown territory. However, this is what I do to calm my own nerves (which crop up A LOT, damn it), and I hope it helps you somewhat too.
1. Have a bath
This is an obvious one. Some people hate baths, but for me, there's nothing more relaxing than soaking amongst some bubbles with a bar of chocolate/glass of wine/cup of tea, watching a bit of Netflix or reading a book. A good way to calm jitters.
2. Listen to something calming
Personally, when I close my eyes and listen to the sound of rain (preferably real rain (although we've had enough of that recently) but I also have a rain sound machine and a few rain sound apps on my phone) I can physically feel myself calming down. I have no idea why, but it works. It may not be rain for you, but it could be the radio. I used to listen to plays at night time - concentrating on the story line forced me not to think about school as I fell asleep.
3. Look forward to something
I don't necessarily mean a specially planned weekend away (although that would be lovely!) - I'm talking on a much smaller scale. I tend to have a TV series on the go (at the moment, it's Grey's Anatomy - starting again from the beginning!) that I can look forward to watching each evening. I can always reassure myself that no matter how awful my day goes, no matter how nervous or worried I am now, there's a blanket, a cup of tea and a good programme waiting for me at the other end of the day. Every day! (Obviously this may be different for you - a good book, or even exercise. Personally, knowing I've planned to go for a run after school would feel me with more dread than reassurance - but each to their own!)
4. Play the "so what?" game with yourself
When @MissDlln tweeted asking for some tips about how to calm her nerves, it reminded me of some advice I received last year. When you're feeling nervous about something and you're not really sure why, ask yourself "so what?", answer your own question, and realise that nothing really has a bad enough ending to be that worried about. Of course you could force yourself down a negative route, but the point is to encourage some positivity. It goes a bit like this...
What if the kids don't listen to me?
So what? I'll follow the behaviour management policy.
What if they still refuse to follow instructions?
So what? I'll call a senior member of staff to deal with it.
What if they think I can't deal with my class because I've called them?
So what? I'm an NQT and I'm learning - they're not going to think bad of me for asking for help. After school I'll ask them how I should've dealt with the situation, although more than likely they will be happy to have helped.
Saying it out loud helps reaffirm things! Because really, you're worrying about nothing, and you will be fine.
5. Look at the big picture
You have trained for months, maybe even years, to be here now. This is what you've been looking forward to - having your own class in your own room. You wouldn't have passed your degree if you weren't capable. You wouldn't have got the job if the school thought you couldn't do it. You've had many placements doing this exact thing - you know you can do it. As soon as the children walk in, you will click into "teacher" mode and it will feel completely natural, as it always has done. Every other teacher has their own worries and will be busy doing their own thing - nobody will worry about the small mistakes you are worrying about making this year! Twitter is the best support network you could have, and if you have had a particularly bad day, there is no better place to vent about it or ask for advice than on there. Good luck and have fun - you will love it!
Find me on Twitter @_MissieBee (previously @Miss_RQT)