Rinse the paintbrush with water until the water runs relativley clear, and most of the pigment is rinsed off of the brush. Be gentle on the bristles throughout this whole process. I drag the brush back & forth on the bottom of the sink very gently.
Put a couple of drops of soap - I use Murphys oil soap, or in a pinch I use a good dish soap - on the brush, and lather on your hand gently.
Step #3: Rinse the brush thoroughly, until there is no more soap in the brush.
Step#5: If you are not going to be using your brush for several days or more, this step is for you only. Just take a bit of the soap, pure, put it on the brush, and shape it so the bristles are perfectly in place. Leave the soap in the bristles until your next use. Keep your brushes wrapped in a clean cloth, or in the original package so it will not get full of sawdust. Just remember to rinse the soap out of your brush before you use it the next time.