1. Create a blank canvas, whatever size you want, and select the rough round bristle brush (part of your defaults).

2. Click the brushes tab on the top right of your screen. A menu will drop down. Check the shape dynamics box and use these settings:

3. Now select the scattering box and use these settings:

4. For the texture box, first save the following image as a pattern by going to Edit > Define pattern. Then use these settings for the texture option.


5. In the dual brush option, you can choose whichever brush you want to mix with the current brush. I chose a premade eliptical soft brush. Just play around with the settings.

6. Skip down to Other Dynamics.

7. Then just check the Wet Edges and Smoothing box.
8. Go click on Brush Tip Shape at the top.

9. Let's save the brush. Click on the little triangle on the Brushes tab and select New Brush Preset.
10. There! Now you have a new grunge brush and are free to scribble all over your canvas. ^^