I like to make a color swatch of each color.  This takes some time but it is fun to do!  You can learn a lot about your colors this way.  I start by cutting pieces of watercolor paper 3″ x 1.5″.

I write the name of the color and the manufacturer of the paint on the back side of the paper.  Then I wet the front of the paper and paint it.  I try to have lay the color on thick and thin to see how dark it can get.  When it is dry I write the name of the paint on the front of the paper.

When I decide on a color, I start to lay the tubes of paint around my palette to see where they will go.