Some artists are still cleaning their brushes in a jar with of Odorless Mineral Spirits, creating a toxic sludge that must be taken to the chemical recycling center. Here's a better way:
1) Go to the grocery store and buy a roll of freezer paper. It has a slick side that will prevent the paint from soaking into the paper.
2) Cut a piece of the freezer paper to wrap around a board. Any board will do. Cardboard, plywood, and craft board all work fine. Tape the paper to the board on the back side.
3) Mix your paints directly on the freezer paper with your palette knife. If needed add a drop of your medium, such as Linseed oil or Spike Lavender oil. Wipe the knife with toilette paper.
4) When changing colors, wipe your brush with toilette paper, or stroke your brush on the paper palette.
5) When you are done, fold the palette paper up and dispose of it or take it to recycling, depending on whether your pigments are toxic. You won't have to wipe your palette board off with solvents. NO OIL SOAKED RAGS TO CATCH ON FIRE.
6) Clean your brushes with soap. Old chunks of hand soap will work fine. Recycle! This assumes that you are using non-toxic pigments in your paints. For example titanium white artist paint is made from the same pigment used in toothpaste. If you are using toxic paints such as those with with lead or cadmium, the leftover pigment water should be taken to recycling.
7) That's It! No toxic solvents to mess with, during or after painting.