A first impression is a powerful thing. In seconds (or less than a second, depending on whom you ask), someone you meet is going to put you in a mental box. Are you trustworthy? Aggressive? Likable?

These qualities and many more are labels people inwardly attach to others when introduced to someone new. But how do you come off in the most favorable light so potential customers, partners, investors, and others want to have a relationship with you?

After years of work helping small businesses manage their relationships with customers, Larry Caretsky, CEO of online CRM software company Commence, has some ideas.

1. Prepare for every meeting.

Even if you've been doing your job for 25 years and think you know everything about your industry, you still need to do your homework. This can be as simple as checking someone's profile on LinkedIn.

"Maybe you are friendly with someone that I've known in the past," says Caretsky. "So now we have kind of a warm connection. You'd be amazed at the value of that kind of interaction. So getting prepared is, 'Whom am I talking with? What is their background? Do we have anything in common? What are their skills and expertise?' Maybe you even worked in the same company at some point. You never know."

2. Display confidence and passion.

The best way to be confident? Know your subject matter cold if you want to inspire confidence, Caretsky says.

As for passion, there's no hiding a lack of it. "[People] see and read body language very, very quickly," he says, "and from the minute you walk in the door: what you look like from the standpoint of a dress code to the handshake that you do to what comes out of your mouth five minutes later. So leadership is critical."

3. Focus on building relationships, not selling something.

Any agenda you may have in meeting with someone should take a back seat to your taking an honest interest in the person.

"You have to be an outstanding listener," he says.

4. Mind your nonverbal cues.

Smile, for one thing.

"I size people up very quickly when they come in and don't seem to be very happy and they're trying to sell me something," says Caretsky. "They shake my hand as if 'Well, I guess I have to shake the guy's hand because that's the right thing to do,' but they really could care less. You get that vibe from someone right out of the gate, and that sets the stage for a very productive meeting or one that's not so productive."

5. Put some thought into your clothing.

How you dress is a big one, as well, and Caretsky recalls with disdain a meeting his team--which intentionally dressed up for the occasion--had with an outside group.

"These guys came in the summer with golf shirts and T-shirts," he says. "So my impression was, 'How dare you come to my company looking like you just got off the golf course? What right do you have to do that?. And it still stays with me. I don't know how many people I've told about it."