Bleegs mapped the opacity of his brush to the pen pressure, it's kind of like shading with a pencil, the harder you press the more opaque your stroke becomes.
By using low pen pressure and the
colorpicker (alt-button) you can "inbetween" your colours.
This is the brush I use most of the time. Dave uses a more oval one and also has his size linked to the pen presure.
Another way is to just lower the opacity of the brush and use the colorpicker, it's more like real paint that way.
Experiment with the brush settings to see what they do.
Smudging I would not pay too much attention to, it a rather messy and slow technique, not recommended for beginners. You can get some nice results by using a speckled brush tip. Using scattering on the smudge tool will give you a smooth textured blend.