Painting loosely does not give you permission to draw incorrectly or to ignore concepts such as form, value, proportion and perspective. These concepts are just as vital to a painting that is painted loosely as they are to one created in a classical realist hand. A loose painting will look primitive and amateurish if your drawing skills are not up to par, it is not an excuse to get sloppy.
As the artist, you must be in control of how much or how little information you choose to include in your brush strokes. That information must always be accurate regardless of how much “detail” is actually provided. You have to get the major forms placed appropriately in proportion to each other; the values on those elements have to be defined so that they sculpt the forms, the perspective needs to be accurate in order to provide a sense of depth. All of these things must be addressed early on in the underpainting stages of the piece.
Efficiency of Brushwork
Looseness and spontaneity come from the handling of the paint on top of a CORRECTLY drawn under painting. To successfully paint in a loose hand, you have to identify the details that really count and figure out what type of brush stroke is going to capture them the most efficiently. For example, the figure on the left in the yellow shirt is wearing cowboy boots with her short shorts (to each their own!), how do I show that without painting every little stitch on the boot? Remember, this is only 5×7, so I have a very small margin for error in getting those boots to look western. In order to successfully do that, I have to pay attention to the exact shape of the toe, notice the point on the foot that is farther back, it says “cowboy boot” from its pointiness.
Also of vital importance when painting loosely is capturing gesture. These figures have to imply a sense of movement–they are not standing still in the middle of 7th Avenue, the are walking at a brisk pace and interacting with each other. The figures in the background move en masse, with just a few that stand out (the bald guy in the blue shirt and the one next to him in the white t-shirt who is walking out of the frame).
When painting loosely, you need to know when to stop. Going back to those boots, if anything adding more detail to them would make them less believeable. You don’t have to put in every stitch, get the form, the values and gesture correct and it will say “boot”, then it’s up to you where to go from there.