I always use a spray cleaner after every use (it only takes a few seconds after you use it to spray it and clean it on a paper towel after you use i...this is a habit I got into when I worked in a department store at a makeup counter, you clean your brushes after every customer and you also spray it with alcohol in front of the customer before you use it on them). Anyways, like I said I use a pray cleaner after ever use, I like the japonesque brush cleaner and if you are looking for something cheaper, the Ulta brush cleaner is not a bad alternative.
I shampoo my brushes once a week. I actually don't use a brush shampoo, I use philosophy's purity made simple facial cleanser. I love this stuff. I use it to remove my makeup at night too. It get's my brushes super clean, is gentle enough for my natural fiber brushes, and rinses easily. Love this stuff. I tend to use a full coverage foundation (Kat Vond D's Lock-It Tattoo foundation), that really can stick to the fibers of my foundation brushes (the spray will get the majority of it off, but it stain's the fibers and sticks to the inner bristles), and the Purity leaves my brushes nearly looking brand new.
Once in a while, if I feel like my natural fiber brushes are getting a bit dry, I will use a light condition to soften the bristles again, but that is very rarely.
Sometimes if I am in a pinch, and dont have my purity, I will use a tiny bit of dawn dish soap. And I treat my synthetic brushes the same way I treat my natural brushes, with the exception of conditioning them.