I don't see what's so hard about this. Be nice. Do not be a doormat. What's a doormat? You go to great lengths to do something for her. If you're working on a big project and she wants you to fetch another assignment for her or get a soda for her, you're a doormat if you say yes. Just tell her you're working on a project and she's gotta wait in a pleasant, but not supplicating way.
e.g. "Hey I'm working on a project here, so ask me later when I'm not busy. Thanks"
Notice I didn't say, "I'll get it to you later." That means you're thinking about this crap all the time. IT's her problem so she keeps track of it.
Now, what is a jerk? A jerk is when you live a block or 2 apart and you refuse to give her a ride in the rain because you're trying to be "dominant." Fvck that sh1t man. Give her the ride, but make it clear she owes you (perhaps pay part of the gas $$$?), and that you're only doing it because it's raining and no one likes to get soaked.
Unless they're naked with you in the tub.
That last comment was some C&F you can throw on top. C&F gets reeeaaallll old reeeeeeeeeeallll fvcking fast if all you say is C&F. No one will call you on it out of being courteous, but I'm just letting you know it's pretty damn annoying. Anyways, all C&F is like sprinkling on top.
Let me repeat that. Your basic attitude around everyone should be a kind, respectful, confident attitude. You obviously can't be C&F with your boss or during a business meeting, but when just chillaxin' you might wanna just sprinkle some C&F in there to COMPLIMENT you already awesome personality. Get it? Good.