The brain makes a judgement about new people within 30 seconds of meeting them, and once an impression is formed it is extremely difficult to alter.
In the world of business, those 30 seconds can be the difference between getting the job or securing the investment, and a lot of hard work going to waste.
Psychologists and behaviour experts explain how to make this briefest of windows count.
A sharp intro
This is an opportunity to convey your value, but must be conveyed succinctly and conversationally.
"Have a planned, practiced self-introduction," says Susan RoAne, communication expert and author of "How to work a room". "If you know how you want to introduce yourself, that will help others respond similarly."
The RoAne Rule is that an introduction should be seven to nine seconds long, customized for specific events, and should give the "benefit of you" rather than your title.
Forget how you feel
Amid the stomach churning and sweaty palms of an important first encounter, put yourself in the other person's shoes.
"In the discomfort of a new meeting, you may be absorbed with how you are feeling about yourself...comfortable, energized, nervous, intimidated and so on," says Ann Demarais, founder of First Impressions consultancy. "After getting more comfortable you may relax your self-focus and turn your attention to how you feel about the other (and) how they respond to you."
"If you can shift your attention from your own feelings to making others feel good, you'll likely make a better first impression."
Social 'gifts' such as sharing stories and encouraging body language can help.
No fiddling. No gadgets.
Over-activity can indicate anxiety and insecurity.
"When anxious, we often fidget or touch ourselves for reassurance," says body language expert and author Patti Wood. "Minimize acts such as rubbing your ear-ring or moustache, twisting your hands, pushing back your hair, and so on."
While ignoring your phone can be a challenge, it can also be rewarding.
"In this electronic age, with so many distractions, it feels great when you have someone's full attention," says Wood.
Match their body position
Open, confident body language is important, as is holding eye contact with a steady - but not confrontational - gaze. But one of the most effective body language techniques is to replicate the other person's.
"Mimicking the posture of someone you meet, whether standing or sitting, communicates empathy," says Jayson DeMers, founder and CEO of social media marketing firm AudienceBloom. "This can help put the other person at ease."
Be ready for anything
You can't completely control the other person's perception of you, but you can cover as many angles as possible.
"Putting in the effort ahead of time always pays dividends," says behavior expert Jez Rose. "Consider what the person or people you are meeting will expect from you, in terms of how you dress and what you bring and then try to go one step further...Effort rarely goes unnoticed."
"There is no such thing as too early... All too often I've planned to arrive at a meeting two hours early and taken a book to read or work to do while I wait, but due to unforeseen circumstances arrived just in time."