THOUSAND PALMS, Calif. -

Can we really judge a book by its cover? When it comes to making snap judgments about others, it turns out, we may be pretty good at doing just that.

We've all heard the truism, "You only make one first impression." It's true -- and these impressions may be more powerful than we would imagine.

Our brains take in a huge number of verbal and non-verbal cues almost instantaneously when we meet someone (or just look at a photo of them) to calculate powerful impressions that are often as accurate as the impressions we form over longer periods of time.

Research has shown that we can make first impressions in just fractions of a second, and not just from meeting in-person. We make fairly accurate first impressions based on simply looking at Facebook photos, and women can tell if a man will be a good father simply by looking at him.

Whether it's a job interview, a first date, or simply an introduction to a friend of a friend, first impressions are incredibly powerful and they can be nearly impossible to reverse. But it's not totally hopeless: Knowing how snap judgments work can give you a better sense of what kind of one you're making.

Here's what you need to know about first impressions -- and how to make a good one.

They happen incredibly quickly.

2006 Princeton University study found that it takes just one-tenth of a second to make judgments about a person based on their facial appearance. Judgments -- on measures of attractiveness, likeability, trustworthiness, competence, and aggressiveness -- made within this span of time were not significantly different than those made without time constraints. In fact, confidence for some judgments actually decreased with greater exposure time.

The researchers found that attractiveness and trustworthiness are the qualities we judge most quickly.

And they're very difficult to change.

First impressions are so powerful that they can trump even undeniable fact and prior knowledge, research has found. A recent study found that when told a person's sexual orientation, participants still identified whether a subject was gay or straight based on their first impression of how they looked, regardless of whether this judgment contradicted the information they had been given. While making quick first impressions is a natural cognitive response, these sort of snap judgments can, of course, lead to stereotyping.

"We judge books by their covers, and we can't help but do it," researcher Nicholas Rule of the University of Toronto said in a statement. "With effort, we can overcome this to some extent, but we are continually tasked with needing to correct ourselves."

A number of factors play into our first impressions. 

When it comes to job interviews or important introductions, the way you dress and the firmness of your handshake could make a big difference in the first impression you make. A 2009 study published in the journal Personality and Social Psychology Bulletin found that both clothing style and posture played a role in initial perceptions, while another study found that handshake strength also affected first impressions. A weak handshake can create the impression of passivity, researchers found -- so make sure you have a firm grip.

The tone and tenor of your voice also plays a significant role in determining what kind of first impression you make on others. A Scottish study found that participants overwhelmingly agreed, based on hearing a subject's voice, on a number of personality judgments, including trustworthiness, aggressiveness, and warmth.

“[Psychologists] have confirmed that people do make snap judgments when they hear someone’s voice,” Drew Rendall, a psychologist at the University of Lethbridge, told Science Mag. “And the judgments are made on very slim evidence.”

To make a good first impression, do it in person.

series of University of British Columbia studies found that first impressions are formed differently in person versus online or by video. The research on over 1,000 participants found that in-person and video impressions were similarly accurate in judging various personality measures such as extraversion and likeability. However, passive video-based impressions were overwhelmingly more negative than impressions made based on meeting in-person. Another study found that first impressions made based on Facebook photos were as accurate as in-person impressions, but they tended to be substantially more negative.

"If you want to make a good impression, it is critical that it is done in person,"University of British Columbia psychologist Jeremy Biesanz said in a statement. "More passive impressions are substantially more negative."

There's one trait we particularly value when it comes to first impressions.

We value trustworthiness over confidence when creating impressions, creating more positive impressions of those we believe to be trustworthy. And this judgment accounts for a large portion of the impression we form, according to social psychologist Amy Cuddy.