When using the two bucket method, or especially if you're just using one bucket when washing, don't forget to drop a Grit Guard into the bottom of the bucket to help keep the dirt down at the bottom instead of getting churned back up into the water.
The Grit Guard is a simple baffle that sits in the bottom of your wash bucket and prevents all the dirt that's fallen out of solution from being carried back up where your wash mitt can pick it up again.
Remember, the goal when washing is to get the dirt and other loose contaminants off the paint, and keep it off the paint.