There are quite a few shortcuts for the layers palette, the most important ‘everyday’ ones are to change layer opacity without using the slider at the top.
Changing layer opacity quickly is important when using Photoshop - but it’s really annoying having to go over to the slider at the top of the layers palette. It’s so much better to just keep an eye on the image and use keyboard shortcuts!
Just use the normal number keys - used individually they alter is 10% increments. So, for instance 5 = 50% and 3 = 30%. If you type two numbers together quickly you can get precise figures - ‘45? gets 45%. This also works with brush opacity, so it’s a great little shortcut to remember!
If this doesn’t work, I’ve found that switching to the move tool by hitting V always seems to make the layer opacity shortcuts work.