Learn a handy keyboard shortcut to merge two layers in Photoshop
One simple trick but one that comes in handy constantly for me is merging two layers into one in Photoshop. This trick can save your life with so many Photoshop projects that require two images to be merged to a single layer.
Make sure the layers you wish to merge are on top of each other in the Layers palette. Click on the thumbnail of the top most layer of the two you want to merge.
Press Control/Command + E.
Now your layers are merged.
Something to keep in mind is the new layer when it does merge will take the name of the layer on the top.