There are many ways to clean brushes. Many brush-centric (MAC, Shu Uemura) companies sell accompanying brush cleaners while some make brush soaps (Becca). I've always shied away from them because the cleaners include alcohol, which I believe damage the brush hairs in the long run. My method takes longer, but ensures that my brushes are baby soft no matter how many washes they go through.
I treat brush maintenance with the same zealousness as my haircare routine. I use whatever shampoo and conditioner I have in my current rotation to clean my brushes. Just wet it, lather up, rinse under warm water, condition, then rinse again. Be sure to hold your brush head down while washing so water doesn't seep into the ferrule and weaken the glue that holds the hair together. I dry my brushes over the edge of a table to maintain the shape. If you think about it, the process is almost exactly like washing hair.
Since I wash my hair with Shu Uemura Cleansing Oil Shampoo (we have to talk about this one day. For now, one word: awesome), I have perhaps the world's most pampered brushes.
I took an hour to thoroughly clean thirty brushes. Bending over the sink wasn't fun, but the waking up to a row of like-new brushes the next morning? Priceless.