Some additional notes in case you are not using house paint...
For Acrylic Paint, water and soap are sufficient. Be sure to clean your brushes as soon as you are finished using them. Acrylic dries very quickly and so brushes can be soaked in water temporarily until you are finished with them. Although dried acrylic paint can be pulled off the bristles, it will probably remove a good portion of them and leave plastic residue. This being said, acrylic brushes are pretty durable, and even when they get frayed and worn still work fine - in fact shorter bristles can help push the paint around easier.
For Oil paint, clean the brushes using mineral spirits (less stinky/toxic than turpentine).
For Watercolour paint, brushes are quite easy to clean with a little water, and soap if necessary. However, they are probably the most delicate so should be treated carefully.
Some good general rules:
- Do not leave paintbrushes in water for extended periods of time - this will swell the wood and ruin the shape of the brush.
- Paintbrushes should always be washed in cool water - never hot, as it actually can cause the glue to loosen and the metal holding the bristles to expand, causing them to fall out.
- Work the paint out from the ferrule to the tips.
- A good brush cleaner is "The Masters" Brush Cleaner, sold in most fine art stores.
- Brushes should be stored bristles up in a cup, or lying down.