Until you get to know someone, your brain relies on snap judgements to categorise him or her, predict what he or she will do and anticipate how you should react.

You may have heard that a person only has a few seconds to make a first impression, but the truth is your brain makes up its mind about a person (so to speak) within milliseconds of meeting him.

According to research by a Princeton University psychologist, this is an evolutionary survival mechanism. Based on the information it has (how you look), your brain decides whether you are trustworthy, threatening, competent or likeable, among other traits.

One way we can hack this split-second judgement is to be aware of our body language—especially in important situations. Whether you’re applying for a job, asking for a raise or meeting a new client, being mindful of our body language can influence others perceptions of us, as well as outcomes.

Here are 15 body language blunders to watch for:

1. Leaning back: You come off as lazy or arrogant.

2. Leaning: This can seem aggressive. Aim for a neutral posture.

3. Breaking eye contact too soon: Doing so can make you seem untrustworthy or overly nervous. Hold eye contact a hair longer—especially during a handshake.

4. Nodding too much: You look like a bobble-head doll. Even if you agree with what’s being said, nod once, and then try to remain still.

5. Chopping or pointing with your hands: This feels aggressive.

6. Crossing your arms: Doing so makes you look defensive, especially when you’re answering questions. Keep your arms at your sides.

7. Fidgeting: Fidgeting instantly telegraphs how nervous you are. Avoid it at all costs.

8. Holding your hands behind your back or firmly in your pockets: Doing so can look rigid and stiff. Aim for a natural, hands-at-your-sides posture.

9. Looking up or around: This is a natural cue that someone is lying or not being himself. Try to hold steady eye contact.

10. Staring: Staring can appear aggressive. There’s a fine line between holding someone’s gaze and staring him down.

11. Failing to smile: If you never smile, you can make people uncomfortable and wonder if you really want to be there. Flash a genuine smile, especially when you meet someone for the first time.

12. Stepping back when you ask for a decision: This move conveys fear or uncertainty. Stand your ground, or even take a slight step forward with conviction.

13. Steepling your fingers or holding your palms up: Both of these gestures look like begging positions and convey weakness.

14. Standing with hands on hips: This is an aggressive posture, like an animal puffing itself up to look bigger.

15. Checking your phone or watch: You’re signalling that you want to be somewhere else. Plus, it’s just bad manners.

So, what should you do?

Whether you’re sitting or standing, aim for good posture in a neutral position. Stand with your arms at your sides, and sit with them at your sides or in your lap. Naturally hold eye contact, smile and be yourself.

If you have a particular problem with one of the gestures on this list, practice in front of a mirror or with a friend who can remind you every time you slip up. Do this until you become aware of the bad habit.

Bernard Marr is a globally recognised expert in strategy, performance management, analytics, KPIs and big data. He helps companies and executive teams manage, measure and improve performance. A version of this article originally appeared on LinkedIn.