Holding eye contact all the time during conflict can be a mistake as it can escalate the tension if neither of you is willing to break. 

The goal isn't to never break eye contact but to know what your behaviour signals to other people.

• Hold eye contact if your priority is to show you're not intimidated.
• Look down if your focus is to de-escalate and defuse the situation.
• You can hold eye contact for three to five seconds, then break to the side instead of down.

You can project confidence without speaking. Being non-reactive in situations where most people would lose it shows you feel confident in your ability to handle whatever is happening. 

The goal here isn't to fake that you're okay while freaking out on the inside. It's to cultivate a genuine deep internal confidence.

Gail up your hand gestures when you're speaking to more people. 

Show conviction with your words. When you speak about your plans for the future, don't say "I hope" or "I want" but "I will".

Show conviction with your tone. Turning your tone upward makes statements sound like questions. This gives the impression that you're unsure of yourself.

• Take a pause when people most want to hear what you have to say.
• You may worry that speaking slowly and pausing a lot will lead to people cutting you off. You can prevent this by continuing to speak in that same slow-speaking cadence until you're finished with your sentence.
• Don't shout. Quiet words can carry massive weight.

For example, focussing on "I" is not very persuasive if you want a raise or promotion from work. So instead, focus on the value you can add to the company by playing at a higher level.

Work with your boss to create a concrete list. At the same time, go out and get other job offers. Then, if they want to back out from the agreement, you can tell them that you want to stay, but you have other offers that pay more.