Not that I have always followed my own advice.
Possibly my worst teaching moment was when a student in the front row started searching through her purse, eventually pulling out a pen and yellow sticky note. I found her lack of attention distracting but managed to carry on lecturing...but then she scribbled a note on the sticky pad and pushed it towards me. I said something like, "Just hold your questions for a moment, until I get through the next few slides" but she persisted in pushing the note at me, even lifting it off the desk and waving it a bit. Highly annoyed at her impatience, I snatched the note and read out, "Your fly is open."
Moral: It really pays to take student questions as soon as possible.