I work in a small team of four people including myself, only ever 3 of us in at the same time. The people I work with are all brilliant so that helps a lot. I keep myself hydrated drinking 3 litres of water when in work. Have a few cups of coffee each day as well. Eating well is one crucial one for me as well, if I've not eaten enough or not for a while then I notice that I can get quite moody, can't concentrate as much and become tired. As little as 5 minutes after eating I notice a huge differance to the amount and quality of work I do.
Still looking for another job though as I want something that pays more and is more interesting as well as giving me a bigger work load. As strange as that may sound I don't like being at work with nothing to do and clock watching.