To copy and paste Layer Effects (Styles) from one Layer to another, Control (Mac) | right -click (Win) the “fx” icon on the Layers panel and select Copy Layer Style from the context sensitive menu. Then, select the layer(s) that need the Layer Style applied and Control (Mac) | right -click (Win) to the right of the layer name in the Layers panel and select Paste Layer Style.
Or, it might be easier to place all of the layers into a Group and then add the Layer Style to the Group (instead of adding the Layer Style to each layer). That way, if you have to make changes to the Layer Style, you only have to make the change to the Layer Style on the Group.
Because the Layer Style was applied to the “Fish” Layer Group, the Layer Style is automatically applied to all three layers included in the Group. Notice how the large “fish” on the left has a gradient and pattern overlay while the two other “fish” (whose layers aren’t included in the group) do not.
Any layers that I add to that Group will automatically have the Layer Effect Applied.
Here, all of the layers that make up all three of the “fish” have been added to the “Fish” Group, so they all have the same gradient and pattern overlay (because Layer Styles applied to a Group are automatically applied as additional layers as they are added to the group).
One word of caution: if you have layers within the Group that overlap one another, Photoshop is going to act as if all of the layers within the Group are merged and then applies the Layer Style. In the illustration below, see how repositioning the two shapes in the Layer Group so that they overlap creates a very different result than when the Layer effects are added to each individual layer.
In this example,the same layer Style is applied to each plant layer.
In this example, the Layer Style is applied to the Layer Group. Notice how it appears as if the three plant layers are merged before the layer style is applied.