Hi Karen,
I have painted in acrylics almost exclusively for the last 15 years because of a bad reaction to the solvents contained in oil paints. I have found many great tips in Golden Paints web site
www.goldenpaints.com. Suggest you look carefully at their color mixing guide as it provides some very good tips and practice recommendations. I substituted Pyrrolic Red Light for the Napthol Red Light as I wish to use the most permanent colors possible. Other than that I found that I could mix virtually any color I needed with only the six recommended colors plus titanium white. I also found it helpful (although somewhat tedious) to create the color mixing charts that Richard Schmidt recommended in his book "Alla Prima". A great exercise for learning to work with your selected palette. Wish you success. Acrylics are a great medium once you learn to work with them.