This is the most time consuming part. Once you have blotted out your colors and materials, it’s time to create a new layer and make it all come together. Customize the texture to fit your model. You will need a graphics tablet for this.
Turn off your UV layer if you have not already, create a fresh layer, select a rough brush (I like to use the charcoal brush) and set the opacity jitter control to pen pressure so you have direct control.
Try to find the lightest color on the canvas and use your color picker to sample it, make a color swatch somewhere on an unused bit of texture space so you can easily and quickly pick it again when you need it, do the same for the darkest color. Make sure your dark color is not very saturated.
Start by carving out the details and destroy obvious shapes that run across multiple rocks or cracks and edges to get rid of that slapped on texture look. Pick up on some of the highlights and shadows on the edges and define them a little more. Keep sampling right off the canvas and only go back to your swatches when the canvas colors are too subtle.
Use your swatch colors very sparsely to define some deep crevices and strong highlights.
Take your time, work loosely and start with a bigger brush, then go smaller and smaller in brush size.
At this stage you can also define the edges of your model a little more by increasing contrast between…
light and dark around an edge using subtle gradients.