Reddit mentions of Portrait Painting Atelier: Old Master Techniques and Contemporary Applications

Working cools vs warms is a little complicated. I recommend buying some painting books and color theory books to really know what I'm talking about. Basically decide what is going to be the structure of your painting, value or warm/cool shifts. So lets say you decide value (basically you'll find a lot if values, strong darks and lights). Warm/ cool shifts in this context could mean: most of the shadows will feel cooler than the lights (or vise versa). The way you mix that would be: shadows made of violets, greens, blues + a slight neutralizer (the opposite color) or a shade like black, or grey and the lights with bright versions or the hue shifted to things like red, yellows, oranges. (Know that context determines whether a color feels warm or cool. blue can be warm if surrounded by certain neutrals etc etc) However, instead of painting the shadow of on an arm brown, paint it violet. Warm cool shifts work best when there is little value. So if the shadow is Waaaaay darker than the highlight, don't push the violet too much. But let's say you decided to have little value in a painting and wanted space to be formed through warm/cools then make the highlights from red tints and the shadow from violet with no change or little change in value. You see this type of painting Impressionism to contemporary work and prior to Impressionism most painting is value based (due to pigments and the color theories of the time). Extreme values make an easy read for a work, while warm/cools play tricks on the eye and are visually unstable, which makes a painting visually develop over time (stand in front of some Rothko works and you'll know what I mean). It really depends on what you're going for. Also paint from life. Photos flatten things out tremendously and you'll see a lot more color and dimension from actual observation.

Color theory book I recommend: The Elements of Color:

1. A Treatise on the Color System of Johannes Itten Based on His Book the Art of Color
   http://amzn.com/0471289299
   
   
2. Interaction of Color: Revised Edition
   http://amzn.com/0300018460
   
   
3. Interaction of Color: Revised and Expanded Edition
   http://amzn.com/0300115954
   
   Painting technique book I also recommend:
   Portrait Painting Atelier: Old Master Techniques and Contemporary Applications
   http://amzn.com/082309927X
   
   Sorry I'm on mobile and 3:30am so I am a but too exhausted to make those clickable. I look forward to seeing more of your paintings :)
   
   A Cezanne portrait where his colors in the face do what I'm talking about (using color to make planar shifts or space) http://www.canvasreplicas.com/images/Paul%20Cezanne%20Self%20Portrait.jpg
   
   A Degas based on warm cool shifts: http://uploads3.wikipaintings.org/images/edgar-degas/the-pink-dancers-before-the-ballet-1884.jpg