Adding urban flavour to your artwork is easy. Derek Lea defies convention with the Brush tool, and explains how pre-sets work.
Photoshop's Brush tool doesn't necessarily have to be used for painting. It can be a useful stamp for creating instances of stencil or stamp art as well. Instead of painting a stroke, you can use a single mouse-click to create an impression of your brush tip on the canvas. Granted, it doesn't sound too impressive until you imagine using compelling artwork as a brush tip instead of a hard- or soft-edged ellipse. Arguably the most important thing to consider, in addition to the technique of stamping instead of painting, is that you need to get your artwork on the tip of that brush.
Defining a brush tip from your own art is an essential part of the process, but chances are you'll have many different stamps you'll want to use at different times. So rather than defining custom brushes each time you wish to use them, you should acquaint yourself with the different preset options available in Photoshop. When you define a piece of artwork as a custom brush, it will be added to the list of available presets in the Brush Preset Picker and the Brushes palette.
There will be times when you want only your own brushes to appear within the list of presets, saving you sifting through all of the others. Also, the need to save your new brush libraries will present itself. In order to address both these issues, you'll need to familiarise yourself with Photoshop's almighty Preset Manager.