This technique starts with pre-wetting the wood.  I like using a 2nd paint brush, dipping it into the water and then 'painting' the wood with water.  

Then taking a second paint brush, I paint a section of the wet wood with Chalk Paint® decorative paint.  A small amount goes really far.  When you're no longer able to spread the paint, grab a towel and start wiping off.

After finishing the whole surface, step back and look at the whole piece.  If there are spots with more paint than you like, brush on some water, spreading the paint thinner, then wipe off with a towel.  

Conversely, if there's a spot with less paint then you like, dip your brush in a little water, a little paint, and re-paint that area, spreading the paint around.  Then dry with a towel.

This is a fast project and usually by the time I'm done with 'washing' on the paint it's ready to be waxed.  

Remember - You're washing the color into the grain.  You aren't painting the piece.  You want the grain to show through.  

This oak cabinet door was washed with Chalk Paint® Graphite and finished with dark wax.

This barn wood bar was washed with Chalk Paint® French Linen, finished with clear wax.