1) From a sports photographer: Use of the back focus button. Huge improvement in focus accuracy and shooting speed. [thanks Seth!]
2) From a wedding photographer: Shoot in full manual mode. All the time. Of course this is how I worked for years in black&white with manual cameras, but I'd gotten lazy/complacent/trusting of the camera. No more. [thanks Tara and Ben!]
3) From a sailing photographer: Push the histogram to the right. I had always treated digital files like slide film as opposed to negative film, making sure not to irretrievably blow out the highlights. No more. As he pointed out, I can pull beautiful detail out of a hugely overexposed RAW file, but trying to pull up muddy shadows just results in noise. [thanks @onnevanderwal]
The difference in recent images is astonishing. An my respect for these pros who give so freely of their expertise knows no bounds.