Good characteristics are always a great winner.
Displaying confidence is a big one. If you don't know how too here are some good ideas of self confident gestures. Smiling, eye contact, relaxed, Head up, shoulders back, keeping your hands out of your pockets, not crossing your arms, longer steps, etc.
Sense of humor. Don't be a class clown, but just know how to laugh, smile, and be funny sometimes.
Comfort. Being comfortable around others is a big one, but being comfortable around yourself is a bigger one. In order to be comfortable around other people (girls) you need to be comfortable with yourself. Learn to love yourself is what is say. Don't go out and be a cocky douche bag though. Just know yourself, be yourself, and love yourself. Show your comfortable around girls by smiling a lot and laughing at fun stuff. Be the guy at the movies who laughs at something funny in a comedy movie, be the guy who's at the amusement park getting excited for a scary ride. Just enjoy yourself and girls will definitely enjoy you. They will see your comfort all over your face and will want to hang around you. Honestly girls love a guy who smiles because he's projecting comfort. So just be fun and smile.
Have adventure written on your forehead. Bring the adventure to your relationships with girls. Don't be "that guy" be someone fun and exiting, keep her guessing. The last thing you want is for her to know you like the twilight book she's been reading...yea she'll get bored of you quickly. You want to remain a bit mysterious and fun. Ex.) Tell a girl "you're seeing" that you are taking her out Saturday evening but don't tell her where. This will keep her excited and on her toes. She will want to know what you have planned. But make sure you have known the girl for a while before you do that. Take her out on planned things first, and then when you think she's comfortable, give her a surprise. Go ice-skating, boating, to an amusement park I don't know just something like that...but make sure it's something she'd enjoy. And don't tell her where you're taking her.
Style. Have some style to you. Upgrade your wardrobe. Go to the mall and get some nice jeans sunglasses, shirts,
Hygiene. Look nice, smell nice. Remember to shower daily. Brush teeth daily, maybe get some teeth whitener. Shave. A lot of girls appreciate a well groomed man. If you're real hairy you might want to shave. I shave my chest and face and trim other areas.
Go to the gym. get some lean hard muscle. Eat good and sleep better.
Go buy some nice cologne. I have used the same cologne now for 5 years, it's my signature scent. The price was 90 dollars but it lasts me between 6-7 months and I wear it daily.
Gather up some hobbies that suit you. Find your talents and get good at them. Play guitar, get in a sport, cook, build stuff, be a nutritionist, get into art classes, etc. Those were just examples. Just do what you like to do and girls will take notice.