Good posture goes a long way in how others perceive you and how you perceive yourself. Standing up straight portrays confidence and high self-esteem whereas slouching portrays low self-esteem and unprofessionalism.
Be aware of how you're walking. Relax your shoulders and roll them back. Keep your head up as if a string has been pulled through the center of your spine, standing you up straight. Lillian Glass, a body language expert says, "Confident people are always looking up, never down at the table, the ground, or their feet." 
Having great posture is the first step in portraying more confidence within yourself.
2. Plant your feet in an open, wide stance.
You are now aware of your posture. Now what? Pay attention in how you are standing. The correct stance can demonstrate confidence. Stand shoulder-width apart. When you are standing with your feet too close, other people will assume you are timid.
In a group setting, if you want to see who's interested in you, focus on where their feet are facing. If someone is looking at you, but their feet are facing elsewhere it means they are not that interested in you. To show interest in others, angle your feet in the direction of the person talking. When you do this, you are portraying trust and openness.
3. Hand Motions with Open Palms
When speaking, be sure to incorporate your hands. Provide subtle hand motions that show your palms. The goal is to have smooth, broad hand motions when talking to others. Showing your palms to others represents honesty and openness.
"So, if you come with palms up you show that you're trustworthy, honest and have nothing to hide." 
Tip: Do not move your hands too fast when speaking.
4. Keep Your Hands Visible and Out of Your Pockets
When you are speaking or listening to others, always make sure your hands are visible. Keeping your hands in your pockets can be seen as unconfident and a sign of defensiveness. Hiding your hands can also subconsciously portray to others that you are lying or "covering up" something.
5. Eye Contact
Strong eye contact when talking or listening to others is essential for showing confidence. If you are uncomfortable with doing this, start small. Look into their eyes for 2 seconds then look away (upward and to the left). Build yourself up where you can confidently and comfortably look at them while you speak for longer periods of time.
Tip: Make sure to do this naturally and do not force it or else you will come across as creepy.
(Bonus) Eliminate "filler" words. Not only do people measure confidence in the way you look, but people measure confidence in the way you speak. It's crucial to be aware of how you speak to others. To be more confident when speaking: