You’ve got smarts and skills in spades, and you’re brimming with potential. Still, in a high-speed, hyper-competitive business world, you have little time to make a big impression. You have to project credibility in an instant or risk being overlooked or rejected.

Today your credentials may get you in the door. Yet to really succeed, you’ve got to look credible when it matters most: in face-to-face interactions. Whether you’re meeting one-to-one or presenting to a packed audience, your credibility is immediately being assessed.

But what does credibility look like? And, more important, why do some smart, capable people project credibility, and others—who are just as smart and capable—don’t?

In studying this phenomenon with thousands of clients, I’ve identified 25 specific visual and auditory cues—explicit “codes of conduct” for posture, gestures, vocal skills, and eye contact—that affect the perception of credibility. And unlike countless other cues, such as gender, age, or physical features, these 25 cues are within your active control. What’s more, small changes can make a big difference.

To get started, consider these seven dos and don’ts:

1. Do keep your head level.

In the dog world, renowned trainer Cesar Millan has exceptional “executive presence.” Dogs recognize his alpha status by the way he carries himself. In the business world, one of the best ways to project such presence is to keep your head level when speaking—no raising or dropping your chin, which can appear aggressive or submissive. The power of this one skill—to literally be levelheaded—can be transformative.

Fast Tip: Lengthen your spine and level your head. Now, moving only your head, like a camera on a tripod, scan your environment while keeping your torso still. Stillness is an authoritative behavior, so try not to let your shoulders twist with the movement of your head.

2. Do keep your hands in the gesture box.

In poker parlance, a “tell” is a subtle signal revealing the strength or weakness of a player’s hand. Similarly, in meetings or presentations, your gestures alone can be telling to others. The most effective hand gestures happen inside the “gesture box”—no higher than your sternum, no lower than your hips, and no wider than your shoulders. The sweet spot is your navel, where gestures tend to look the most natural.

Fast Tip: A common tell of self-consciousness is when your mouth is engaged but your body language isn’t. To appear comfortable, get your hands involved immediately, reaching out to your listeners with interactive gestures. In short, if your mouth is moving … so are your gestures.

3. Do speak with optimal volume.

If you’re a Seinfeld fan, you surely remember the infamous “low talker.” Likewise, in business settings a common problem with volume is speaking too softly or dropping volume at the end of sentences. The good news is that volume is the easiest vocal skill to adjust. First, however, you must know the difference between adequate volume and optimal volume. Most people err on the side of merely adequate. If you want to be a powerful voice, speak with a powerful voice.

Fast Tip: Your diaphragm, the small muscle separating your chest and abdominal cavity, is your engine for volume. Strengthen this muscle with five minutes of isolated exercises a day. One such exercise: Say the days of the week in a single breath, drawing out the vowels to prevent your diaphragm from resting between words. Later, move on to the months of the year.

4. Do hold eye contact for three to five seconds.

“Eye contact is the best accessory,” says writer Takayuki Ikkaku. It is also a key indicator of confidence and credibility. Still, there is a difference between making eye contact and holding eye contact. Duration is critical, and in the Western world, holding eye contact for three to five seconds is considered optimal.

Fast Tip: As you converse with coworkers, try speaking one phrase to one person. Then, when you reach a natural pause, speak the next phrase to someone else. Continue in this way, letting the structure of your sentences guide your rhythm. You may look away momentarily, but keep your eyes on the horizon—no looking up or down—and each time you come back, hold eye contact for three to five seconds.

5. Don’t use speech fillers.

Speech fillers are superfluous sounds or words, like “um” and “you know.” Today, such fillers are pervasive in our culture, including the business world. A smart, young technology CEO recently said to his team, “So, I actually sort of passionately believe that we have an opportunity to, uh, you know, sort of really take this platform to a new level. So we just kind of, uh, need to jump in, you know, with full force.” He wanted to fire up his people, but his fillers extinguished his passion.

Fast Tip: Embrace the tactical pause. Instead of interjecting fillers, simply pause while your mind searches for the next word.

6. Don’t make extraneous movements.

Extraneous movements—such as jiggling your knee, bobbing your head, or shifting your weight—weaken your personal power. You might say, “I can’t help myself. I just can’t be still.” Truth is, excessive fidgeting is a self-comforting behavior. Stillness sends a message that you’re calm and confident.

Fast Tip: Test your ability to literally have a level head. Fold a thick pair of socks and balance it on your head. Try talking for several minutes without losing the socks.

7. Don’t make yourself smaller.

If you’re like most people, when you feel intimidated, you make yourself smaller so as to avoid being an easy target. You might place your feet closer together, tuck your arms to your sides, dip your chin, or pull back on your volume. Any or all of these behaviors say, “I feel threatened.”

Fast Tip: Practice optimal standing posture throughout the day, not just in important situations, to help make it habitual. Balance your weight over your feet, lengthen your spine, and elongate your neck.

About the author: Cara Hale Alter is president of SpeechSkills, a San Francisco–based communication training company, and author of The Credibility Code: How to Project Confidence and Competence When It Matters Most (Meritus, 2012).

About Vishinda: Vishinda is a NYC wholesaler of fine cut white diamonds, and offers a calibrated diamond service for sourcing matched pairs and layouts of ideal cut diamonds according to mm size.