Here is a quick guide to how I use Brush Dynamics in Gimp 2.8. (This is assuming that you have a drawing tablet that is already configured with Gimp, The Google is the best sage if Gimp is giving you tablet woes.) I've been getting questions about what brushes I use. I mainly use a plain circle brush for everything and just switch the dynamic. Square/rectangle brushes make pretty painterly backgrounds, though.
I've been through different phases of what brushes I use or what dynamic settings I like. My preferences will probably change again in a few months
. No brush system is going to work for everyone, you just have to play around with the settings until you find what works for you, but maybe this tutorial can be a starting point if you don't know where to begin.
Other tutorials: [link]
(There are a total of three at the moment...