Admitting I'm wrong or that I screwed up, and likewise praising others when they're correct or have ideas I agree with. You would not believe how much smoother everything at work is when you learn to recognize early the signs that you're holding on to a bad opinion, or that you're headed towards a fuckup, and just saying it out loud. The praising / agreeing thing is a bit more complex. I've noticed more recently that…
I try to make it more meaningful by saying why I agree with or like something in order to clarify the (prefferably shared) values behind my appreciation.
I've also recently used a torrent of appreciation (the Mesita strategy) to build up the self-esteem of a person struggling with self-confidence.
The trick is it has to be honest and at least somewhat meaningful to them (it's not good to compliment someone on things they don't value).
A really over the top example: complimenting a woman in the workplace on her looks. will definitely not be appreciated and these days might get you fired ;)