well first of all you see a lot of people all at once and you don't notice everything about each and every one of them. so first there has to be someone that catches your eye and that may not always be physical, maybe it's something they're doing or the way they talk that makes you look at them a little more. It could be their best or worst trait that you notice first, but once you start looking you look at everything. The way a guy carries himself is what attracts me most, their gestures. I look at their hair (I love long hair), their arms and hands, face, and the way they're dressed.
about a week ago I saw a guy at school and he came out of nowhere walking in front of me so I only saw his back, but the first thing I noticed was how tall he was (I like tall guys so that's what I usually notice first). then I saw his long wavy hair and the way he ran his fingers through it =] (even the way he walked was sexy) I looked at his arms, his clothes, his boots and I totally forgot where I was going. but I never got to see his face, not even a glimpse of it, and that kind of bugged me.
I would say the paper bag on her head. I would notice that first. If she didn't have a paper bag on her head then I would notice her face. A pretty smile and eyes really get me. The body usually follows. Then find the mean of both scores and that is where she stands on a physical scale.
When you first meet a person, you don't just stare at their body first, or just their face. You look at absolutely everything, from their arms to to their face to their overall body figure to their hair and god knows what else. You never notice only their face first, or only their body. You notice something different first with every person you meet.
The first thing I always notice is how they guy carries himself. I do admit the next thing I notice is how he looks, but its mostly how he carries himself and what kind of "air" he gives off. That's what mainly attracts me.