In an interview it’s not just about what you say but also how you act. Body language says a thousand words about who you are, your confidence and your passions. The hiring manager sitting across from you can 
learn a lot about you from your handshake, posture, eye contact, hand fidgeting when you talk and facial movements. Be aware of your own body.
1. Eye Contact.
Maintain good eye contact from the beginning to the end of the interview (with balanced breaks otherwise you’ll appear creepy). Don’t let your eyes wander around the room or stare at you hands. Strong eye contact shows that you are confident, listening, and engaged. Remember to smile and this will be reflected in your eyes.
2. Handshake.
The introduction. The first impression. To communicate yourself as confident your handshake should be firm, but not knuckle-breaking and definitely not a limp, dead fish. Practice with your family members to find the perfect balance.
3. Expression.
Be in control of your facial expressions. Studies have proved that wearing a smile makes people feel more positive and confident event if its not true. Be animated when you’re talking about things that you’re passionate about. The hiring manager will feed of this energy and it will leave a strong impression.
4. Posture.
The ideal posture is a neutral position. Do not not slouching or lean back against the back of your chair as this implies you’re overly relaxed, arrogant or simply just not that interested in the job. Conversely leaning too far forward is a breach of their personal space and could be construed as too aggressive. The perfect posture is to straight up on the chair with a slight lean forward to express you’re interested and engaged.
5. Arms.
Never have your arms crossed in front of your body. This sends a message that you are feeling defensive. Keep your hands relaxed hands to your sides when standing or on your lap/knees when sitting.
6. Excessive Nodding & Fiddling. 
Keep all body movements calm and considered. Don’t nod your head continuously as the interviewer talks regardless of how much you agree with them. It will only look ridiculous and over enthusiastic. Furthermore pay attention to your extremities like leg twitching, over gesticulating with your arms and nervous fiddling with your hands. Maintain control of your extremities, sit with assertion and confidence.