The most important thing a singer can do is warm up. Without a proper warm up, you're going to cause damage at some point, even if its just wear and tear. Pro athletes always stretch and prepare before doing anything, and as a singer you’ve got to do the same. Singing is demanding on the vocal cords. When you speak, you use a limited range of pitch and volume. However, when singing, you could be sustaining a high note one second, and the next note will be an octave lower. Also, many times you’ll be screaming a note and the next note will be as soft as a whisper. To get this kind of control, you have to complete an adequate warm up.
The best way to begin a warm up is by doing vocal trills. Vocal trills induce whats called vasodilation. This just means that the blood flow is going to your vocal cords more quickly, better preparing you for singing. To do a lip trill, let your lips vibrate like you're imitating a horse or motorboat. At the same time they are vibrating, you’re also going to produce a pitch. Its best to do these on 3 and 5 tone scales so that the focus can remain on form rather than executing an intricate scale.
The next thing you should do is a 5 tone scale on an “AH” vowel, as in father. Do this at around the same volume you speak.If your voice starts to crack, let it happen; pushing will only cause you to either pull chest or crack even more, neither of which will do you any good. Make sure not to get louder as you go higher up in the scale. When you reach your highest note, start descending back to your starting note.
After this, do some jaw/tongue tension release exercises. My favorite is to hold your jaw down; don't force it or squeeze it into place, just let it hang naturally. Do a 3 tone scale on “LAH GAH”. Make sure your jaw isnt moving up and down with each repetition; your tongue should be forming the vowels, not your jaw.
Once you have finished your tension release exercise, finish up with a staccato exercise. The rhythm of the exercise isn’t as important as the form. There will be many choices in the exercise mp3 download section for variations of this. What we are doing though is doing scales on “HE”. This causes your cords to adduct very quickly and efficiently. Make sure the “HE” sound stays very clear and consistent. If it starts to get breathy or distorted, you're doing it wrong. Also, your stomach should not pulsate with each “HE”. If it is, you're pushing too much and need to back off the pressure a bit.
After you've completed your personal warm up, drink some water and take a 5 to 10 minute break before singing. When you're finished singing, take another 5 minute break, drink lots of water, and do all of these in reverse (start on the higher notes and go down; let the high notes be in falsetto when warming down). If you skip the warm down, your voice is going to be harder to warm up the next day because there could be some excess swelling that will only get worse overnight.
This warm up is just an outline. To put together your own personal warm up, work with a vocal coach privately, buy a vocal training system, or you can piece together your own exercise routine through mp3 lessons with myself.
To summarize, a warm up is essential to getting your voice performance ready. Any number of exercises can be used to bring you to this point but a good starting routine should consist of:
1)Aligning breath pressure/cord activation (trills)
2)Opening up the voice/placing tone (open "AH" scales)
3)Tension release ("LAH GAH" open jaw scales)
4)Power activation (staccato "HE" scales)