Studies show that if you really want people to like you as a person, you're actually better off ignoring their pleas of help and making them do favors for you instead ... and just remember to really go over the top in thanking them for it. It sounds crazy, but it has to do with how people don't like feeling that they owe you something, but like feeling that you owe them.
See, the problem with doing minor nice things for somebody is that they forget about it much faster than the person doing the favor. A few days later, the girl has long forgotten the coffee, and the guy quickly gets annoyed that she didn't appreciate it enough. A month later, he's all "BUT I GAVE YOU THAT COFFEE! You owe me at least a hug!" While the value of the gift decreases in the recipient's mind, it actually gets inflated in the giver's mind, until he's equating it with having fought a bear for her. Here it is in graph form:
So it actually drives a wedge between you; the innocent favor turns into kind of a power play. Which brings us to the weird, opposite corollary of this rule, and it comes courtesy of none other than Benjamin freakin' Franklin.
"Game recognizes game."