The easiest way is by using any kinds of brush cleansers.. Im currently using the one by MAC ..
To avoid product waste, I transfer into an empty spray bottle so that I can just spritzz on the brush bristles instead of pouring it into a cleaning bowl.
Spray the dirty brushes and swirl the brush onto a clean cloth.. re-spray with the cleanser and re-swirl until all the brushes are clean~ready to be used. This method is the easiest and the fastest way to have a dry makeup brush for the next usage
Deep cleaning: Once in a while, I clean the brushes thru this method. Pour some shampoo conditioner (any brand) into a clean bowl, and mix with warm water
Deep in all the dirty brushes and let it soak for a few minutes. Next step is hold the brushes under running water to rinse. Make sure all the residues have been removed. Squeeze the bristles lightly, up from the base to the up of bristles to remove any excess water or soap. Lay the brush flat on its side onto a washcloth to dry.