As suggested in another thread, here are some ideas. I'd love to hear what helps others. As a singer and full-time music teacher, this has been a problem for most of my career. The best help I ever got was not from a singing teacher, but from a speech therapist. Here are some tips that keep me vocal:

-Learn to breath from your diaphragm (lower abdomen)- I tell the kiddos to breath from your bellybutton! Never start a song without a good deep breath and keep breathing!! - Imagine the sound coming out of the top of your head. Your throat is important, but you have no control over what happens there. Relax! - Breathe - Keep your spine straight, your shoulders relaxed. -Keep breathing - Smile, or if the song isn't happy, lift the cheekbones a little; it helps project the voice into the resonating chambers, or "loft". Good singers have resonance where their brains ought to be! -Don't forget to breathe!!!!!!!!!!!!