If I have time (and a private place) before I perform, I do the following:
standing up: shake to loosen limbs, then various stretching exercises
sitting down:
5 mins - take several slow deep breaths, breathing as deeply as poss and slowing right down
5 mins - still slow and deep, low humming on out-breath
5 mins or longer - vocalize "maaaa" on out-breath
5 minsscales of some kind (if short of time, do them as a kind of up and down whoop)
2 mins - talk gobbledegook, stretch tongue, pull monster faces, massage face, particularly round jaw.

If little time/private space, I do as much as I can of these without making a complete fool of myself.

Works for me!