Lots of good information, advice and exercises are to be found here:

Breathing/Voice Exercises

Personally, I think regular breathing exercises are crucial in increasing and then maintaining lung capacity, which has a knock-on effect when it comes to "singing loud and long" without damage to the vocal folds.

For clarity, the quickest and most effective (and hence most difficult to master, but well worth it) tongue-twister, which can be done anywhere before performing is to practise saying the name "Peggy Babcock" over and over, faster and faster. That's one that I always do before performing (singing or speaking).

It's good to get together with others to do these exercises - good fun !

- jeanie