Expressive painting 101
Find an image of something you want to paint. I strongly recommend high contrast images in black and white. A high contrast image is one that has a lot of strong dark areas and a lot of light areas. I recommend black and white so that you do not get attached to any colors in the original.
Decide what you are going to paint on. It can be any size or shape you want. I actually recommend working a little bigger as it will make the painting part more fun. The above painting is a piece of 4x4 foot Masonite. Once you have decided what you are going to paint on you need to buy some black gesso and paint it black. A black background is essential for this type of painting because we want some of the black to show through and give the painting a gritty sort of look.
Transfer your image to your painting surface. A white piece of conte or charcoal will be your best choice because it will show up nicely against the black. A projector is essential to transfer and enlarge you image. I use a little projector called the tracer that I bought at Michael's with a 50% off coupon. It is an irreplaceable tool that is worth the money you will spend on it.
Once you have your image transferred it is time to start painting. Get everything set up before beginning to paint. I like to have about 10-15 brushes of all shapes and sizes ready to go so I don't have to spend time cleaning brushes while I am working. When you want to switch colors just toss your paint brush in your water bucket and grab a fresh one. You can clean them all when you are finished painting.
Now for the paints. I squeeze at least 10 different colors on to my pallet before getting started. High viscosity paint works the best but is a little pricey. I like to use the entire spectrum of color so I put a little from each of the color groups plus white. I like bright versions of colors too like lime green etc. My application strategy is simple. Dark areas are painted in cool colors (blue, green and purple) and light areas are painted in warm colors (red, orange and yellow) Use white only to mix with other colors and do not apply it otherwise. Do not use any black paint. Make sure to mix the colors either during the application to surface or beforehand. You don't want to many of the colors to look like they came straight from the tube.
Try your best to finish in one sitting by painting quickly and expressively. Keep a used dish towel to wipe off any paint that has gotten too muddy or that is just not working. Make sure to keep the original black and white xerox or photo handy to look at during the process. I clip it to my painting surface so I don't have to keep looking down at it.
Also, make sure to have consistency in your color choices. For example, I painted John's hand in the painting above red orange just like his face. Since it is still his skin tone it should be in the same color scheme so your viewer understands what it is.
Touch ups. When the entire painting is done there will be areas that don't look right. Go back and make the changes the painting needs. A good way to find areas that need tweaking is to step back from the painting so that all the details blend together. Another way is to take a picture of it and look at it on the LCD of the camera.