To open up requires that you talk to people in the first place. One way to initiate conversations is to talk about things that are capturing both your and your to-be conversation partner's attention. For example, if you are waiting in line at a coffee shop and you are both looking at the menu, you might start with "How is anyone supposed to make a decision between all these great sounding options" or whatever else rings true to you in that moment. Remember to listen carefully to what the person says to you, as this will give you clues about how to follow-up the conversation. For example, if she says "I'm going for the Americano" you might mention another coffee shop that you know that makes a great Americano and ask her if she's ever been. Like it or not, your body language says a lot about you. To appear more open, keep your arms and legs uncrossed while looking directly at whoever you're talking to. By adopting an open posture you will come across as more positive and open and will not seem closed off or arrogant, which can help when looking for people to interact with.  Open, expansive posture can also make you feel more confident and powerful and may help you act in more open ways.   Part of open body language is smiling. Smiling is a very social emotion and you will seem more approachable with a grin on your face. To begin practicing opening up, you need to engage in honest, open conversation. Try asking someone a question such as, “How are things going at work?” instead of “How’s it going?” to get an open answer.   Then, in turn answer open-ended questions honestly, instead of with trite statements like “Fine” or “Ok.” Or, you might ask, "What's something wonderful that's happened to you lately?" or, "What activities would you recommend in town?" Asking people personal questions is not always appropriate; however, in most cases people will be flattered that you are showing interest and listening to them. Try connecting with someone over hobbies, interests, family life, vacations or books by asking about...

TL;DR in Indonesian:
Bukalah percakapan. Praktikkan bahasa tubuh yang terbuka. Ajukan pertanyaan terbuka. Carilah minat yang sama. Kembangkan sikap terbuka. Cobalah mencontoh orang yang sangat terbuka.