A first impression may seem like a 'hi, whats your name and what do you do?'.
But you actually use your eyes for first impressions. Everyone will look at something first and something second before getting a proper first impression, but you can sometimes be wrong by just looking at their face.
The very first thing I notice about people I just met, is their legs. I know it sounds weird, but their legs. When I started school, I looked down at the teachers leges and thought, 'She looks nice, but I wonder if she is.' And then I slowly raise my head, scanning their entire body. I then either say hi to them, or wait until he/she asks for my name.
The second thing I notice about people is hair. A quick glance at their legs, and then a speedy lift of my head, allows me to look at their before I look back to their legs.