Working on a layer that is not the top layer

Hi, have been using PS for quite a while and have learned to do many things but still seem to be missing a basic understanding of layers.

If I create a new layer and clean up a photo with spot healing brush tool or whatever, then add a hue and saturation layer and then filters or whatever.

Then I want to do a little more clean up on my first clean up layer - then how do I do it?

Moving the layer to the top allows me to do it but it disables all the lower layers and if I make the clean up changes and then put it back to its original position then the new changes don't show.

Maybe I l learned many more advanced things and simply don't know how to do one is hopefully one of the simplest.

Any help would be much appreciated ...

Michael PS CC