1) Studying Opera to Sing Other Styles
This belief is not as prevalent today as it was in years past, but it still exists. Everyone has heard a classically trained singer attempting contemporary music (it was even the subject of a running skit on "Saturday Night Live"). Men will often sing with an overdarkened, heavy sound, while women will bring their head voice far too low, and both are completely inappropriate for most modern styles.
The problem is greatest for women. In terms of vocal acoustics and registration, the female classical and contemporary voices are very different. Broadway belting requires a much stronger and extended chest voice (the lowest register of the voice) blending into a strong head voice (the highest register). This blending area becomes crucial, because if the singer takes the pure chest voice too high, vocal fatigue and damage can result. Unfortunately, this is often what happens, as traditional training does not address this intense, chest-driven singing. The singer often pulls her chest voice in a desperate attempt to compete with skilled belters.
I believe a singer should study what he or she is going to sing. Find a teacher who works in contemporary styles and who can show you how to blend head and chest voice together to eliminate vocal strain.
2) Trying to Sing from the Diaphragm
This is a well-intentioned but often misguided attempt to find vocal power and balance. The idea comes from skilled singers who feel a pressing or support in the area of the diaphragm when singing. The problem arises when the inexperienced singer tries to apply the same intensity. The rush of air against the vocal cords often causes the singer to either break apart or jam the cords together in order to resist the air pressure. Vocal imbalance soon results. The vocal cords cannot handle large amounts of air early in the training process. Remember, power comes from how much air the cords can skillfully resist, not how much air you send them.
3) Going for Power Too Soon
This is tied into the previous mistake of pushing too much air. Vocal power comes from balance, and balance takes time and skill to achieve. Patience is well-rewarded in vocal studies.
4) Trying to Place the Voice
This is an issue of cause and effect and putting one before the other. Most singers have been told to "bring your voice forward" or to "place it further back." Unfortunately, most singers have no idea how to accomplish or control this, leading to various degrees of vocal imbalance. The fact is, this "placement" is a result of resonances in the voice—where we feel the vibrations of the sung note. The way to control this is through vowel adjustments. Wider vowels, such as "ah," will tend to bring the voice forward, and closed vowels, like "ooh," will tend to sit the voice further back. Using subtle shades of vowels will give the singer different tonal colors, as well as a sense of having the voice placed in different areas. Control the vowel, and the placement will take care of itself.
5) Dropping Keys to Avoid High Notes
This one can be deadly over time. One of the core problems in contemporary singing occurs when singers take their chest resonance or lower register too high. The result is serious vocal strain. Singers will try to get around this by dropping the key until the high notes are at the top of where they can pull up the chest voice. Over time, these notes become more difficult and the singer must drop the key again, creating a cycle of vocal abuse and diminishing range.
A good approach to this is to temporarily raise the key of the problem song, forcing the singer to find a lighter, more balanced vocal mechanism with which to sing the high notes. When going back to the original key, the singer often finds a more balanced and easier approach to the problem notes.
6) Letting Style Be a Collection of Weaknesses
I find this to be more prevalent in pop and jazz singers, as these styles allow for more vocal improvisation. Singers will make musical decisions based on their need to avoid certain notes or vocal demands, such as sustains. They will go breathy, cut a note short, or do a musical run down the scale and away from the high, sustained notes. Even though experienced singers can sell these tricks to an audience, they impinge on your ability to give your all to a song. After a while, the lack of range, power, and balance becomes apparent to the more sophisticated listener.
7) Not Studying with a Teacher
The most important thing a good voice teacher can give you is instantaneous feedback with a skilled pair of ears. The human voice is a very sensitive instrument; very small changes can yield great differences in the result. Consistent study with someone who can quickly help the singer make these adjustments and point out when balances are correct or incorrect is essential. A good teacher will help the singer advance quickly and avoid serious vocal trouble.