Being smitten with a girl at first sight can deprive you of your common sense. You're probably going to be so nervous or excited that you can't rely on your own judgment to tell if the girl is open to you. So, it'll help to keep in mind some general points on body language.
Experts emphasize the importance of eye contact. One method is to casually make eye contact with a girl across the room. If you catch her eye, offer a warm smile and hold for a second. If she looks back again within a minute (with a smile, preferably), she's likely interested, or at least open to you [source: Lowndes]. Try initiating a conversation.
Expert Patti Novak says to keep this conversation light and causal -- avoid intense subjects, like politics or religion. If you listen attentively, take heed of her interests, and use that to think of a good first-date idea. If she loves art, for instance, ask to take her to the latest exhibit at the museum.
Pick-up artist Neil Strauss also says to keep it casual. He's so adamant about it, in fact, that he doesn't think a guy needs to ask a girl out on a date at all -- at least in the traditional sense. It's too uncomfortable to sit across from a stranger for two hours over dinner as you evaluate each other, he maintains.
Instead, if you want to get to know a girl better, you should invite her to do a task with you that you need to do anyway. Strauss gives the example of shopping for shoes. "That way, the focus," he says, "isn't on you two -- it's on the task." You also could ask the girl to a dinner party or any group event with more than four people. Whatever it is, it should be quick and fun, according to Strauss.