A mistake I see time and again in beginning and intermediate singers is "the wandering larynx."
Laryngeal stability, like vibrato, is a tricky subject, because too much attention brought to the subject can be just as problematic as too little. BUT, it is a simple fix that can reap incredible benefits on the sound, and ignoring problematic laryngeal positioning is disasterous.
So let's talk about the positioning of the larynx. It's yet another example of "The Three Bears" in singing, but this time there are four options... For simplicity's sake, let's call them, from lowest to highest:
Lowest -- depressed larynx
Comfortably low -- appropriate for classical sound
Moderate -- appropriate for non-classical sound
Highest -- raised larynx
Let's tackle the extremes first... Position 1 -- the larynx is pressed down too low. The sound is woofy, way too dark, phonation is uncomfortable, the tongue root is tight, etc. Position 4 -- the larynx is way too high, and the resultant sound is "necktie tenor," childish, nasally, bright. So neither Position 1 or Position 4 are ever desirable, except *perhaps* for comic effect.
Position 2, sometimes called the "comfortably low larynx," is one of the pillars of good classical sound. Position 3, a moderate position of the larynx, is a totally healthy location for the larynx, and renders a sound that is more appropriate for pop singing, folk singing, musical theater--basically all non-classical genres.
So, when you hear musical theater being sung "too operatically," it's highly likely that one of the primary issues is that the larynx is too low--it's in Position 2 rather than Position 3. The reverse is true--when you hear "popera," and the sound is too poppy for the genre, the larynx is likely in Position 3 rather than Position 2.
Within either genre, singers need to be aware of certain situations in which the larynx tends to rise. As pitch ascends, it is very common to see a singer's larynx rise. Especially when pitches leap up suddenly, it is all too easy and tempting for the larynx to pop up to try to "reach" the pitch, as if it is "up there" somewhere. A good fix for this is to go back to the beginning of the phrase and breathe in the position of the highest note--thus, you're ready far in advance for the leap. Another way to practice is with pitch glides. Start with small pitch glides, something like 1-5-1, keeping the larynx in a comfortably low position. Then gradually expand the glides, keeping the larynx comfortably low. Also, it is critical to let the larynx rock and tilt within all of these positions--the larynx needs to be free to make subtle adjustments within the positions described above.
Caveat 1: There is also a vogue of artificially darkening the sound, especially among low-voiced male singers. In other words, baritones wanting to sound more "manly" by singing in Position 1 when they should be in Position 2. This is to be avoided, as it makes a fake sound and can "shave years off of careers!" I have observed that younger singers too often sing with a higher larynx than they should, and older singers too often sing with a lower singer than they should.
Caveat 2: Any experimentation with laryngeal positioning should be done with supervision of a competent teacher.
Kyle Ferrill teaches voice and vocal pedagogy at the University of Memphis, SongFest, and the Interlochen Arts Camp and performs around the country, primarily in art song and oratorio.