The image you give to other people is key. I actually met my girlfriend because she began approaching me first, then we got to talking, and things went from there. But it wouldn't have happened if I'd been physically unattractive.
I have some acne, but in my experience, a lot of women in my age range (I'm 22) don't care too much about it. Even so, I try my best to take care of it with skin products. Shaving regularly, diet and exercise are worth it. You don't have to be sculpted like Apollo or anything - just get yourself into a reasonably attractive shape if you aren't already. Skinny isn't bad at all (I'm on the scrawny side). Even hefty can work, especially if you have some muscle to back it up. Also, the clothes, as they say, make the man. You don't have to buy name-brand stuff, and in fact, often it's better if you don't. Get some stuff that flatters you, and remember that that doesn't always necessarily mean dressing nice. A ratty old hoodie and a dirt-stained pair of blue jeans works for more people than you think.
I see you're old enough to drink, so going to the bar with friends is a good idea, even just to people-watch. Practice conversation with people you trust. Being confident around people of your own gender is a huge first step in being confident around the opposite gender.
As far as what to say, what questions to ask -- people like it when you ask about them. What does she do for a living? Where did she go to school or college? What was her major in college? What are her hobbies, her interests? Does she have a favorite book or movie? If you've never read or seen it, what is it about? Why does she like it? When she replies, try to ask another question, avoid saying "Well I like..." in response as much as possible. An interested woman will ask you the same questions. If she asks them first, ask them back.
This bit's difficult for people with AS, but try your best to consciously focus on eye contact and body language. Nod, chuckle where appropriate, say "mm-hm", listen and show her that you're listening. Leaning forward slightly is a tell that someone is interested in what you have to say, for instance.
Above all, remember: There are a lot of men WITHOUT Asperger's Syndrome who are no good at dating, so you're far from alone. You're also no less of a man, so be confident! Dating and relationships are an art, not an exact science, and like any art, the more you observe, the more you learn, even if you can't quantify what you've learned.