When you think about it you can't discuss brushes without discussing ignorant bandleaders who think the only way to achieve a softer dynamic is to demand that the drummer play brushes. Thats not what they are for.
Brushes provide a range of colors,everything from Brazilian to Rock. The one thing about brushes is that there is really no accepted technique for playing them. It's all ear, feel and imagination.
The best thing to do is to listen to the great brush masters like Papa Jo Jones (Jazz), Don Um Romao (Brazilian) and Russ Kunkel (Rock). There are many others, of course, but you have to do the research.
Jimmy Cobb once stated that Elvin Jones can be easily identified playing brushes because he plays the whole cymbal beat on the snare. Thats a good a place to start. Play the cymbal beat with one hand and a smooth sweep in the other. What you will get is your first lesson in swinging with brushes and layering your sound.
Once you get the groove down then you can start changing pressure on the head and decorating your groove with accents and sweeps. Remember the sky and your ears are the limit.
The groove continues...