What is the best way to clean my brushes after painting?

The best way is to wash your brushes in warm soapy water, making sure that you get all of the paint out, then let them dry naturally. I like to lay mine flat on a towel to dry. I understand that Murphy's oil soap will salvage brushes that have had paint dry in the fibers and the art supply stores do sell special brush cleaning soaps as well.

But, if you wash them right after using them, you should be fine. Pay special attention to the “heel,” the part of the brush that comes out of the “ferrule”. This is where paint tends to build up and dry. Once this occurs the bristles of the brush will separate. See diagram below.

A trick that I learned is to dip the whole brush in water before I start working. This keeps the paint from drying in this heel area and will allow you to more easily wash it out at the end of your painting session. Remember, if the acrylic paint remains damp it can easily be removed from the brush.