One of the best vocal workshops I ever attended was an NAC (National Association of Choirs) event in Kidderminster last year. The workshop was divided into different sessions, one of which was given by a young local singer for would be soloists. What I found most interesting was the advice she gave about warming up your voice and good breathing technique before you begin a session, whether it be a concert or just a rehearsal.
I had heard of the concept of circular breathing before, in relation to instrumentalists, but she talked about a similar technique for vocalists. It basically involves you breathing through your mouth (better for singers than nose breathing as it fills the lungs more completely) dropping your jaw as if to yawn and pushing it forward as you breathe in. What surprised me is actually how effective this technique is, and how it has not only improved my phrasing as I can sing for longer without taking a breathe, but also it has improved my swimming technique as I can hold my breathe longer under water!! Great advice, go and try it out!!