Summarize:

This technique works great with rough or reclaimed wood. The finished product will look rustic, and will look like the wood of a barn. Because this technique is designed to create a rustic look, you almost never have to sand. The roughness of the wood actually adds to the final, barn-like, product. The wood does not need to be perfectly clean, but if it's very dirty, wash it with soapy water. Let it dry completely before you begin painting. It is best to pour the paint on the center of the wood. Start with a small amount, and add more if necessary. You can use any type of paint with this technique, although most people find latex paint the easiest to work with. Add water if the paint is too thick. Adding water will also make it easier to drag the paint across the wood. Spread the paint across the wood, into the grain, and let it soak into the grooves. If you want a light coat of paint, you can spread the paint out thinly. For more coverage, don't spread the paint as widely. Repeat this step to fill in blank areas. Let the piece sit overnight, and then check it. The paint may take longer to dry in areas where you applied thick layers of paint. Make sure it is completely dry, and not tacky to the touch, before you move the wood. If you want the wood to have more coverage, or a brighter finish, add more paint and scrape it across the wood. Add as many layers as you like, but remember that the more paint you apply, the less the wood will show through.
Use the paint and drag technique to create a rustic look. Pour a small amount of paint directly onto the wood. Use a wide putty knife, or scraper to drag the paint across the wood. Let the wood dry for at least 12 hours. Repeat as necessary.