When you’re not confident and a bit nervous, your voice tends to stay in a higher register. It’s not always easy to detect when it’s happening. Make a conscious effort to keep your voice a bit lower, whether you notice that you speak in a high voice or not. If you know you feel uncomfortable, pay attention to how your voice changes. Lower the pitch of your voice, in addition to the volume if that’s an issue for you. In other words, speak up! This will tell others that you view your voice as worthy of being heard. And then they’ll be more likely to follow suit, thinking the same. Much like how our voices raise when we’re nervous, they tend to speed up, too. So the next time you’re in front of class giving a presentation, slow down. Slow way down. Slow down to the point where you think you’re going too slow – odds are then you’re doing it just right. This technique is also known as “slow talk.” You can practice it by reading out loud to yourself.  An unconfident person wants the moment to pass as quickly as possible and get over it – hence why they speed up in the first place. To fake confidence, slow down, giving off the impression that you're comfortable basking in the spotlight. Confident people are more likely to be assertive and use "I" statements. Instead of "You make me angry," which is quite passive, a confident person might say, "I am angry with you," which is much more direct and cutting. To feign confidence, talk about yourself. No one else is going to! It's nice to ask questions about those around you, definitely. Everyone appreciates a good listener. But you've got to be an active part of the conversation, too, by speaking. If something comes up that you can relate to, talk about your experiences with it. The person you're talking to just saw your favorite movie? Instead of, "Oh, what a great movie!" you might say, "I love that movie! It's my favorite. I just saw it for the umpteenth time last...." Being negative, nagging, and spreading gossip about other people indicates a lack of confidence....

TL;DR in Indonesian:
Turunkan volume suara Anda. Berbicara dengan lebih pelan. Gunakan pernyataan dengan kata "Saya" . Bicarakan hal yang positif dan hindari gosip. Jangan melantur.