First of all, congrats on the job!
I have a desk job and have had for quite a while. Some advice:
1- I work out at a gym 3 to 4 times a week. Boy, do I feel better!
2- Its okay to get up and take small walks. The brain is an organ and needs blood to function. Increasing circulation makes you think better, hence more productive. In the summer time, I will take brief walks outside. (You remember "outside," right?)
3- Bring healthy things to snack on, if you are a snacker. I also bring my lunches. And diet drinks.
4- I have a tennis ball at work that I squeeze as a stress antidote.
I am sure that there are plenty of other things that you can find for yourself.