Tricky question because of the infinite amount of variants involved in the minds of women. No two are the same and no woman is ever looking for the same thing every day. So, hold onto your pants because this answer is going to be long...
To start let me give you the wrong answers that everyone always gives:
Humor, Kindness, Hotness, Great Hair, Money, Romance, A Great Laugh, A Big... uh Car..., Loves Kids, Eye Color, and etc.
Why are they wrong? Because these are things girls are attracted to in guys, its not necessarily what they are looking for. There are variant levels of attraction and at each level you must be willing to look at each woman and understand what she may be looking for. One woman may be ready to find a new life partner while the one right next to her may have just gotten out of a relationship and needs to find herself. So be sensitive to the situation a woman is in but be a man in the sense that if you want something you go out there and you try your hardest to get it. So:
Level 1 : The Attraction
This level is reserved for mainly physical or shallow attraction. Its what I would call the "getting her attention" phase. Because that is what you need to do. Unlike men, women have hundreds of suitors approaching them and vying for their attention every day. Sadly you don't have the luxury of being able to walk by a woman and have her understand the person you are deep down.
1. Confidence : Now confidence is not arrogance or cockiness. It's the underlying idea that you are not in need of a woman, you just want one and you can find one anywhere. The truth lies in this, confidence can be seen from across a room. A man in the center of a conversation and making people laugh is always viewed as the confident one, the man sitting in a corner booth under shadows and watching conversations happen from across the room doesn't exude confidence.
2. Attractiveness : This is also much different than the ideal of drop dead perfect genes. Look toward GQ and Esquire on what it means to take care of yourself. Get a haircut that actually is meant to be on your head. Get a $100 suit and spend $75 getting it tailored (it'll make it look like a $800 suit). Learn how to use cologne. Learn how to handle yourself, the way you walk, dance, and speak are all attractiveness factors. If you look like you take care of yourself, you look like you can take care of her. It's that simple. (By the way this factor is usually what people confuse for women wanting tons of money, they want to be taken care of, it's different).
Level 2 : The Spark
Now, unlike guys a woman can be completely attracted to a guy and not need to instantly fly to his bedroom. A woman's attraction opens her up to the spark. The spark is where you seperate yourself from the crowd of other men. This is where you need to step out of the shallowness and really show her where you are special, what inner talents, skills, or passions you have are to be used to do the following:
1. Make her feel special : If she doesn't feel like she's special what is the purpose of being with you? Don't be afraid to let her know (in a creative and not just literal way) why you are interested in her. Calm down, don't go writing love sonnets just yet, you've got to get to know her first.
2. Make yourself look special : Bring her attention to that which separates you from the crowd. What do you have that no other man has? It better be more than the shallow stuff because you've got a lot of people out there better at it than you, unless you are Justin Timberlake. Do you have an affinity for charity, do you love your mother, do you write music, etc.
3. Now connect the two : Show her how you are connected. Girls want a connection. They want to feel as though they could marry you but don't want to feel like you are pressuring them for that yet. How will your being together rewrite the stars and spawn a whole book's worth of love poetry because the world will rejoice in the union of your two souls?
Level 3 : The Relationship
Now that you've secured her phone number or the date or whatever you can begin on this level. It's time to start to see if you are meant to be together. What do girls want at this point? More than a hundred thousand things always in perfect balance and different focuses based on what her day / week / month / year / or life has been like. A woman who needs to hear "I love you" five times a day one day can need a few days without a single call from you on other days.
What does a girl want then? The answer is your responsiveness to her needs and for you to not give up on her. That's it. You can be funny, charming, strong, fragile, serious, angry, or a host of every other 100% opposite feelings as long as you are being real with her. The greatest part of a relationship is tied to the most frustrating part. The closeness needed for a strong relationship can only come out of fighting to understand that other person and how to meet each other in ways that you both need.
In this stage you have to ask yourself: Is she worth it? Even when we are fighting or going through a rough patch do I still want to be with her? If you cannot answer yes to both of these questions, you need to let her go. This too is something a woman looks for.
In truth the hardest part of any of this is the willingness to put yourself out there. Because when you're out there you can get rejected and it hurts, a lot. You can be afraid, and to be honest sometimes I still am, but the truth is that real confidence is the courage to be scared of something but go do it anyway. I'm not telling you that if you do these steps you won't get rejected, because any time you deal with women you will. But getting out there is the only way to find confidence. Good luck.