One of the most frequent things you’ll find yourself doing with layers in your Photoshop document is changing blend modes to something like Multiply (great for shadows) or Overlay. Moving your mouse over to the Layers panel and clicking the blend mode drop-down menu, then scrolling down to your desired blend mode can be tedious… especially when you’re experimenting and don’t know which one you want.
You can quickly change the blend mode of the active layer by changing to a tool that doesn’t already use blend modes. I just hit the V key to switch to the Move tool, or the M key for the Marquee tool. Then simply hold the Shift key down and tap the + or – keys to cycle between the different blend modes.