Use eye contact.
Get her attention by making eye contact with her. Once you get that connection, gaze deeply into her eyes. Don't stare for long periods of time; doing that may give her the creeps. Catch her gaze, stare deeply into her eyes, then quickly shift your focus from her eyes to her lips and then back to her eyes. Don't look at her body; that could be a turn-off.
Give her a warm, friendly smile. This will certainly catch a girl's eye and let her know you are interested in getting to know her.
Avoid using stand-offish body language.
Don't sit with your arms crossed or with your back turned to the girls you're trying to attract. This will show that you're not interested and don't want to be bothered -- which are not the signals you're trying to send.
Dress the part and practice good hygiene habits.
Girls are attracted to guys who take good care of themselves. When you go out, make sure your clothes are wrinkle-free and you are freshly shaved, smelling and looking good. Your first impression is a lasting impression.
Girls are attracted to guys who are not shy and who are are sure of themselves.