here's a pic of what they look like and some good colors
first, choose the 13px brush and set the hardness to 0. then go to the brushes presets(top right) and click shape dynamics (note:shape dynamics should now have a check).
then do these presets:
Brush Presets
Size Jitter: 55%
Control: Fade & 70
Minimum Diameter: 11
Angle Jitter: 9
Control: Off
Roundness Jitter: 35
Control: Fade & 25
Minimum Roundness: 23
then choose new brush from the little drop down thingy and give it a name and then you're all set!
to make the brush bigger, simply choose a larger brush and then add these presets that are listed above.
this size is good for effects on a lot of things, such as cars and text