It's arguably the hardest day of the school year. You don't know your students and your students don't know you. Eventually, you'll all work your way into a comfortable rapport.
But not on the first day.
I struggled for about seven years before I figured out the first day of school. (And by "figure out," I mean that I came up with something I was happy with.) So here's my advice for the first day of school.
DON'T spend half the period mispronouncing your students' names. It's a time-kill and a first day of school buzz-kill. The students are fairly jazzed about returning to school, and there's a honeymoon going that first day. No need to squander it tripping over all those "tricky" names. You quickly transform yourself into the classroom dunce. It doesn't inspire confidence, doesn't really doesn't serve much of a purpose.
DON'T spend the entire period going over the class rules. What a way to crush the first day. You know those inservice meetings you're required to attend at the beginning of the school year--the ones you have before students show up? You know how they suck the life out of you before you even see your students for the first time. Yeah, it's like that, except now you're doing it to your students.
On the first day, students don't know how your class works. They have no context for your rules. How many classes do you suppose they have where they're NOT expected to be in their seats and ready for class when the tardy bell rings? Do you really need to pound that in on the first day? Let the class operate a little bit, and bring in the rules and policies as they become relevant.
DO cool stuff on the first day of school. Let your students know why your class is the grooviest class on campus. It is! You know that, but they don't know that. Don't keep it a secret. "Tease" them with hints and glimpses of the topics that will be covered during the year. Pose questions that you have no intention of answering until later in the year.
When the end of the first day comes, they should jostle out of your room energetic with anticipation of what your class holds for tomorrow and for the rest of the year. They should be talking to each other about what you presented.
I would hold off on any kind of demo or activity that might intimidate students. That is, hold off on the counter-intuitive stuff. There will be time for that later. You don't need to make them "feel stupid" on the first day. Many are already intimidated being in a class called "physics." Don't scare them off on Day 1.
Have some fun on the first day. Get into your schtick! There will be time to learn the names and discuss the policies. Later. On Day 1, make them eager for Days 2 through 180. It's better for your students and it's better for you.