One thing I have learned about voice over warm ups over the last few years... The sillier you look doing them, the better they are. Well, that is not exactly fact based but let me know what you think after this post. Here is a list of some of my favorite and fast vocal warm ups to get you sounding your best on the microphone.
Put a wine bottle cork or pencil in the front of your mouth and hold with your teeth. While holding the item begin reciting tongue twisters and articulate as best as you can. Continue to do this for a minute or two, if you question the effectiveness of this exercise read something out loud when you are finished. You will be amazed at how clear and crisp everything sounds.
Often times if you are doing an audiobook, commercial and industrial work you will need to be able to read run on sentences without audible breath. One exercise you could do everyday to improve your durability is simply taking a deep breath and giving you longest ahhhhh that you possibly can and till every last piece of air has exited your mouth. Do this three separate times each time you do this exercise, once in your highest voice, your middle voice and your lowest voice.
Resonance is the vibrations of your facial bones to give you that deep, rich and warm sound to your voice. I basically have none, but practicing this exercise helps me to create more resonance in my voice when needed.
Breath in a good breath and say "huuuummm" and hold the last m sound until you feel your lips buzzing and hold that for about 15 seconds. Feel it in your mouth, nose and lips.
Now make an "n" sound by touching the tip of your tongue on the back of your upper teeth and opening your mouth. The tongue should vibrate on the back of the upper teeth and you should feel vibrations on the sides of the throat, sinus area and nose bone.
Go back and forth between the "m" and the "n" sound. The "m" should vibrate the front of the face and the "n" should be the back of the face. Repeat this several times once a day or before any voice over or audition.
Your best work is done when you are relaxed. Sometimes I do a few head rolls or yoga moves if I am feeling tense. And if your mouth is a little dry due to nerves don't forget your lemon water! BBQ chips and green apples are also great for ridding your mouth of that smacky noise!