1. Start by doing the Paper tutorial. To start the Rock tutorial you need an image similar to the one below.
2. To add some extra dimension to the texture we will have to create a copy of one of the channels. Make sure your Channels pallet is open. If you don't see your channels go to Window>Channels and make sure there is a check mark next to the word Channels. Look at each channel and choose the one that has the best contrast. Click on that channel and drag it down to the New Channel icon at the bottom of the channels palette (next to the trash can.) You will then have a copy of that channel. In the image below you can see that I have a copy of my red channel at the bottom of my stack of channels.
3. With that channel selected like in the image above go to Image>Adjustments>Levels and adjust the image so that there is more contrast. The more contrast you have the deeper your texture will look. I exaggerated mine in the image below so the texture would be very obvious - use settings that are appropriate for the look you are trying to create. A good thing to do is to create several versions of the tutorial so you can develop a feel for how far to take these manipulations in order to get the look you want.
