Summarize:

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 ahead to actually talking to each other. Consider what you know about her, as that can lead to a conversation. Is she part of the drama club, or does she play sports? Engaging with her about school activities is a great first way to make conversation. You could even try to be funny, but that can be hard.  You could ask, "Is your training on the track team really hard?" or "What did you think of the pep rally?" You could also say something like, "Wasn't the food gross in the cafeteria today? Isn't it awful what they call food?" or "Don’t you think Mr. Harrison looks and sounds a lot like Yoda?" Now that you have some possible questions, find a good time to talk to her. It should be a time when neither of you is hurrying off to class or activities, and hopefully when you’re both alone. It can feel really awkward the first time, but it does get easier. If she really responds and starts asking you questions too, chances are that she is interested in you. If she doesn’t really respond, it’s likely she’s not that into you. For example, if you asked whether her track training was hard, she might say, "Yes, but I love it!" In that case, you could say, "Cool! What do you love about it? I've always thought about getting into running, but it seems really hard."
Make eye contact. Smile at her. Make opportunities for her to talk to you. Say “hi. Think about how to start a conversation. Engage her in conversation.