Next pick the Eraser Tool (set to a big size and with the edges soft) and use it to erase the center and some of the edges of the lines. You will also have to reduce the Opacity of the layer and for a more interesting look duplicate the layer. Move it slightly above the other and decrease the Opacity more for both.
As you do this, you'll notice the lines starting to disappear, but at the end of this tutorial you will see in the final result that the lines will start to be very visible. That is because in time you can go back and adjust each layer to your needs or maybe apply extra layers on top of them to make them stand out.