The previous post on warming up has to do primarily with creating physical readiness. Know that the “warming up of the brain” is more important.
The initial approach to the singing voice must be characterized by thought and attitude that emphasize coordination and integration, fluidity of motion and stability of body, devoid of unnecessary tension. Anything that feels like tension or pressure is too much.
Spend a few minutes gently (not tentatively or guardedly) waking up the voice while placing operative concepts of balance and freedom into the conciousness. The ultimate goal is to be “thoughtless,” but directed and helpful thoughts will allow the warm-up to be effective.