When you’re waiting at customs or immigration, do not talk on the phone! They’ll warn you of this over and over and yet people still get yelled at for this.
You shouldn’t take pictures in the secure areas either. This may or may not be announced but even if not against the rules, why draw attention to yourself.
I’ve been yelled at for using my computer in the baggage claim area before (in the US). No one could explain to me why not, but they’ve told me not to. Once again, why cause trouble for yourself when you might be in a foreign country. The last thing you want is to be detained when you need to be somewhere else.