Check the departure gate, and then GO there and confirm it, and leave plenty of time to do it.
I had one gate listed on my boarding pass (no one should believe that one), then another on the screen – different concourse – and then a third that was the Truth. So this all takes time. Find it first, then hang out.
Years ago I also learned (OK, twice) that you have to be at the actual gate, not the next number. Because the distance between Gate 25 and Gate 26 can be a tram.
What travel lessons have you learned, by doing it right or the hard way? Post a comment here.
Jane's Lessons Learned 
I have learned to avoid any airline other than Southwest. I like to be able to cancel flight, change flights, re-issue expired frequent flyer points, and I especially like nice airline employees.