I tease them and make them return large favors for small ones.
Couple of examples:
#1) A girl I met at a bar had drank too much. We were going to drive to her friend's house to continue partying with two other guys we had just met. I was DJing solo, by the way. Anyway, while we were all in my car, she was getting sick, so I stopped at my house, which was close. I got her water and she was at my toilet for about an hour. One of the guys we'd just met was really sleezy and kept trying to take advantage of her. Anyway, making the story a lot shorter, I got the two guys out of my house and got in touch with her friends to tell them to pick her up. That night could have gone very badly for her, and she and her friends were very grateful I behaved like a gentleman.
So, she invited me to her party a few nights ago. We flirted and kissed, and I kept teasing her about how long I had to clean up my bathroom. She kept apologizing, and I told her she'd have to make it up to me. She kept asking how, so I said she'd have to make dinner for me. I'm going to her place tonight with a bottle of chardonnay (not expensive).
#2) A girl from class didn't buy her book yet. So, she asked to use mine, so I drove out to her apartment complex to study and let her use my book. I was going to study anyway. While we were studying, she kept asking me questions. I kept teasing her, especially about how I not only had to let her use my book, but I had to drive it out to her, and then tutor her! I teased her about being a poor hostess, because I was thirsty. So, she even walked back to her apartment (we were in a study room at the guest house) to get money to buy me a coke from a vending machine. And then I told her she had to take me out to dinner. And when she gave me a surprised exclamation, I told her not to forget to pick me up. Oh, that was after I told her to open my bottle of coke for me.
We're going out this Thursday night.
#3) I told this girl I've been seeing about how girls always take advantage of guys and use them for free stuff. She, of course, felt compelled to defend females. So, the last two times we went out for dinner, she paid without hesitation, even having the waiter sneak her the check.
Just be funny and girls will accept just about any outrageous behavior you can think of.