This article will teach you to clean a paint brush right so you can use the brush for years to come.

Materials Needed:

Dirty Paint brush
Wire Brush
Water for latex paints/mineral spirits or lacquer thinner for oil-based paints
Cleaning a brush / water based paints:

Fill a bucket with clean water and rinse out the bulk of the paint from the brush. Clean the handle as well as the bristles then empty the bucket.
Fill bucket with clean water again. Dip the brush in the clean water then use a wire brush to clean any dried paint on the brush and in the base of the bristles. Brush with the direction of the bristles. Clean all four sides of the brush.
Fill bucket with clean water again. Push the brush into the water forcing the water into the bristles without hitting the brush on the bucket. Do this three or four times and then grab the bristles with one hand and squeeze the water out. Repeat until the water is clear that you are squeezing out of the bristles.

Cleaning a brush / Oiled-based paints:

The cleaning process is the same for oil-based paints as water based except for a few additions issues:

Cleaning agent is mineral spirits or lacquer thinner. Lacquer Thinner is the stronger of the two. You want to minimize the amount used to clean because getting rid of waste thinners is a concern. They are an environmental hazard. Take any waste to a local toxic waste facility.
In order to minimize the waste I will use and reuse my thinners. When I am done cleaning I store the extra thinner in a metal container. If I have purchased more than one container I reuse the container it came in. When I clean a brush again I do the first clean (Step 1) with the dirty thinner.
Thinners can be hard on your skin so wear rubber gloves. Make sure you wash well when finished so as to not get any thinner on face or in eyes.
Clean in a well-ventilated area.

General Information:

Paint brushes come with two basic types of bristles, natural and synthetic. Natural bristles are made from some sort of animal hair, ox hair, goat hair, sable, china bristle, feather, cotton, squirrel hair, and more. Natural-bristle brushes are best for applying oil-based and should never be used with water based paints because they will absorb water and the bristles will become limp.
Synthetic bristles are often made from nylon, polyester, or a combination of both. Synthetic-bristle brushes are recommended for water-based latex paints but can also be used for oil-based paint.
Tip:

Some synthetic brushes can be used to apply both latex and oil-based paints. Be sure to check the packaging on the brush to ensure it’s compatible with the paint you’re using.
When painting it is a good idea to keep the brush submerged in the paint when stopping for more than a few minutes. You will be surprised how quickly paint on a brush dries.