In my years of experience three biggies I often see that hold people back and get them passed over for promotion are:

1. Breathing too high. Train yourself to breathe The number one nonverbal action that most people do wrong at least some of the time is breathe too high in their chest. High chest breathing makes others assume a) you are in danger, b) you are angry, c) you are nervous none of which say promote me.

Training yourself to breathe completely, low and slow into the whole belly will help you look more intelligent too especially if you breathe through your nose. Nothing will make you look less intelligent than breathing with your mouth open. If you have allergies or are an athlete take special note, these are groups that are often susceptible to breaking the breathing-with-mouth-open rule. A bonus to breathing low and comfortable in any situation is more oxygen gets to your brain for clearer thinking and a better quality to your tone of voice.

2. Adopt the right voice pattern for the position desired.How you speak is just as important as what you say. When applying for a service position, you should generally use the “connection” voice pattern – one that is friendly, ending each sentence with the voice going upward, as if you’re asking a question with the chin tilting up just a bit.

For management positions use the “credible” voice pattern – one that maintains a calm cadence, almost monotone, with the chin dipping down a bit at the end. Candidates can use both if the situation warrants it. For example, when discussing your accomplishments for a service position, use the credible voice.
Learn to use both the connection voice pattern (so they can see your human side) and the credible voice pattern (so they can see your position or the position you aspire to). Listeners want to connect with you on both the emotional and intellectual levels. To get a feel for these two voice patterns think about how different a flight captain (credible) sounds from a flight attendant (connection).

3. Speak only as much as necessary and leave your million-dollar words at home. Bottom line, you should be listening more than you talk, but when you do talk, use language anyone can understand. Fancy words, especially when simple words will do, make you sound stuffy, not intelligent. Leaders use words everyone can understand and only say what is necessary to build connection and establish credibility. If you talk too much, you are training others to tune you out. When you do speak, speak clearly and pause in silence (no filler “umhs” and  “ahs”) at the normal breaks in speech.