I disagree with the prior poster who said to dress comfortably. I suggest dressing in a nice suit and tie so you can get upgraded to first class. It also helps if you flirt with the gate agent, they always appreciate the attention, and will show their appreciation by upgrading you.

If for some weird reason you don't get the upgrade feel free to just sit in any empty first class seat you find. If somebody asks to see your boarding pass, just reply "Don't you know who I am?" and then settle back into your seat. That phrase is something of a passcode in the airline industry. Then settle back in your seat and enjoy the flight