Do value sketches.
Simplify your subject.
Do a fairly accurate drawing with good shapes on your paper.
Think shapes, not objects.
Paint from large shapes to small shapes.
Pay attention to edges--hard, soft and lost.
Be sure you have soft and lost edges in your painting.
Paint quickly, but under control.
Get in and get out.
The first stroke is your best stroke; fewer strokes win.
Use the largest brush you can for as long as you can.
Fewer palette colors result in fewer touches of the paper.
Use a spray bottle to help move the paint on the paper.
Paint on an angle to help the color move.
Pick up and tilt your board for even more movement.
Don't worry about "messing up." It's paper, you can always paint on the back.
Don't worry about creating a "good painting." Remove that stress and just play.
Don't render; interpret.
Keep in mind what attracted you to a subject. Stick to that.
Don't give everything the same level of attention.
Don't try to "make it happen," just let it happen. Trust: water, paint, paper and brush.