Size her up but be subtle about it. You don’t want her to think you’re a creep or something. Let your attraction be known but don’t be too overly aggressive about it either. Strike up a conversation with her in the most casual way you can muster. The last thing you want to do is give her the idea you’ve been practicing on hitting on women in front of your bathroom mirror.
Also, lay off the lame pickup lines. “You must be tired because you’ve been running around in my mind all night” just doesn’t work. Start the conversation about sports if you see her wearing some sort of sport clothing. Almost all women are into music, so strike up a conversation about the ridiculous thing Miley Cyrus did yesterday. A playful argument also works to get the ladies attention. Once she starts to warm up to you, use body language to show your attraction. This includes non-intrusive physical contact such as touching her arm. This shows you are confident but you are also comfortable with her. If she reacts to your touch by reciprocating, it’s usually a sign that she’s interested.
This is also the perfect time to drink more because alcohol plays an essential role in doing things that are against your better judgment. If she’s alone, buy her a drink. If she’s with her friends, buy them all a drink. Drinks all around. Just make sure you aren’t too drunk to have a little dessert later in the night, if you know what we mean.