See if she wants to keep your attention or if her eyes move away from yours. If she is consistently making eye contact and sometimes blushing while doing it, chances are she’s interested in you. She may also try stealing quick glances at you when she thinks you're not looking.  Of course, you don't want to just stare at her because that will come off as creepy. Just glance in her direction, or try to hold her eyes for a couple of seconds. However, some girls are just shy, and they may not want to make eye contact with you. Try encouraging her with other steps. Smiling shows your interest, and makes it easy for her to smile back at you. Sometimes, it might take a while for both of you to just make eye contact and smile before you’re ready to actually talk to each other. Even if you’re nervous, smiling is a good way to make contact because a smile actually acts as a reward to other people. In other words, when you smile at her, her brain perceives it as a reward, making her happier to be around you. Don’t just hang around with the same group of friends. It’s much easier to approach someone who is alone rather than someone who's with a large group, so if you make sure you're alone sometime when she's around, she might come over and talk to you. You could also try and go alone to a place you know she will be to make yourself a little more available. You never know what might happen. For instance, maybe you notice she spends time at the library after school. Make it a point to show up there, too. Try sitting at a table near her, where she can see you. ” It’s an easy first step and a way to acknowledge that you’re noticing each other. You don’t have to do much more at first if you’re shy. If she’s unwilling to say “hi” back, she might not be interested. Try it a few more times, but if she never responds, let it go. You might be nervous about approaching her, but the only way you can really test your theory of whether she likes you or not is to actually talk to her. If she’s responded to your greeting, you can move...

TL;DR in Indonesian:
Lakukan kontak mata. Tersenyumlah kepadanya. Ciptakan kesempatan baginya untuk berbicara denganmu. Ucapkan “halo”. Pikirkan bagaimana memulai percakapan. Ajak dia mengobrol.