Be open, relaxed, approachable, friendly, lighten up
0) You can try nlp exercises, meditation, breathing techniques, visualisation. You can read books on this subject and there is a wealth of resources on the internet, youtube regarding this subject.
1) Relax, imagine you're just observing or there as a traveller. For example, if you are on holiday, you go there to experience and observe the attraction, you're not going to get anxious doing that are you?
2) Smile, smiling in contagious.
3) Be confident, respect yourself, accept yourself, work out, wear good clothes, feel good, focus on your passions, know you are a good person who treats people well, you have got as much right as everyone else.
Think positively, be proud of yourself, do things that make you happy, remember your happy times, what makes you confident? What makes you proud? Do you have a skill you are good at? Do things like cooking, driving, learning that increases your confidence daily. Relax.
Have good posture, body language, improve your appearance. Be happy with yourself.
4) Dress well, have good grooming, hairstyle, have good posture.
5) Just say hi or hey to people in your vicinity, who cares if they don't say anything back?
6) Ask how they are, how's everything, how's it going, what's the latest, what made them choose this course, their plans for the future, their plans for the rest of the day, weekend, how was their weekend, their day, what they will get up to, what they got up to, ask them about their hobbies, talk about what's happening. You could read up on current affairs.
Talk about the weather or did you see that sports game? Just mingle with them,
Compliment them, say "I like your jacket".
If you know they went on a holiday or somewhere, ask them about it etc.
7) Be passionate about life.
8) In group discussions, relax and talk to someone close or if someone says something you know, you can talk then. Stay relaxed.
9) Lighten up, have a laugh, laugh easily, be friendly, approachable, interested, relaxed.
10) You can write things down and come up with a rational reframed response, keep a journal of your thoughts, reach out to people slowly