On this quick video Colin Smith from PhotoshopCAFE shows how to better work with layers in Photoshop.
If you have many layers in your workflow in Photoshop Smith has some tips for you in this video.
He starts by playing with a new adjustment layer – but this applies to all the layers below it. However there is a way to work around this. If you hold the alt/option key and drag the adjustment layer only to the layer you want to influence.
There is another way using the square and down arrow icon (see the video to find it). You can also convert a layer to a smart object and go to the image adjustment and choose curves for example and this will only effect a specific layer.