Overview:

Testing different blend modes on a layer can lead to unexpected and delightful results. To quickly toggle through and test various blend modes, have your Move Tool selected (V), and use the hotkeys below:

Mac:

Shift + (plus) = cycles down through blend mode list

Shift + (minus) = cycles up through blend mode list

PC:

Shift + (plus) = cycles down through blend mode list

Shift + (minus) = cycles up through blend mode list

Using the same hotkeys with your Brush Tool selected (B) will toggle through the blends modes of your brush. Happy blending.