First I start by laying out the path of the swale with my trusty A-frame level. I built this A-frame so the legs would be 5' apart and I stick in a flag every time I move it across the ground. This allows me to easily measure the length of the swale by simply counting the flags.

Then I start on the uphill side of the swale and skim off the layer of vegetation, usually a few inches deep and a couple of feet wide. I just roll this material slightly downhill.

They I go back and follow the same path, but digging in about 18 deep with the bucket, trying to keep a gentle angle for water to enter. This material gets dumped on top of the vegatation layer and creates the berm.

In this picture you can see a 5 gallon bucket as a reference to scale.

And finally if you aren't bored yet, I have a time lapse video of me cutting this.