A woman says a lot with her eyes.
Many times, she doesn't even know that many of her thoughts and feelings are being communicated with her eyes. For instance, pay special attention to whether a woman makes direct eye contact with you, instead of glancing around the room or looking at other people in the group. Even if she is not the type of person to look a person in the eye for long periods of time when speaking, she will still hold eye contact with you longer than she typically would. Also, if a woman's pupils dilate when she is speaking to you, this is another sign of interest. The direction of her gaze will also give you clues of her intent. If she glances at your mouth often, it is a sign of attraction as well.
A woman's body language is a major communication tool.
Notice whether she turns her body toward you when you're speaking, or even crosses her legs towards you. Also, if she sits closer to you than she would to a friend or acquaintance, it also could mean that she feels comfortable with you and has feelings for you. Even when a woman is standing in a group, she may turn her body in your direction without even realizing it.
Pay attention to the conversation between the two of you.
Though some women are good at making conversation just to be polite, they cannot fake their romantic feelings for you. If she asks a lot of personal questions and shows a genuine interest in your answers, it means she truly cares about who you are as a person. Also, if she tries to extend the conversation, it means she wants to spend more time with you, which is also a sign of interest.