We used to have a thread on a previous iteration of Polycount where people shared little hidden or hard to find tricks for working with Photoshop. I learned so much from that back then, I thought I'd resurrect it. To share the old information again, but also to see if anything new shows up!
Some tips that were shared back then that I can remember:
-How to change the colour of Photoshop's background, which has now been simplified to just rightclicking on it.
-You can click-drag on the layer visibility icons to toggle multiple ones at once.
One I just discovered is when you're dragging something and hit the sides of the screen and it scrolls, you can hold shift to go faster. I believe the fast behaviour used to be standard (and ridiculously annoying), so I'm glad to see this new behaviour. It makes working zoomed in a lot easier.