Well, I did it for my first time yesterday. I built an A-frame level like this one...
..and staked out a contour line. While doing this, I had an epiphany!
My property is mostly a north facing slope, and while laying out my contour, I realized that if I build the swale with a large enough mound on the downhill side, the area above the "water trough" of the swale will be SOUTH FACING!! So, I'll get naturally irrigated, south facing beds that should be much warmer than the rest of the north facing slope. This is good news, as it's perpetually too cold in my location to grow much without protection. I'll try to get some photos of the process as I proceed.
I used the basic method described here:
http://tilz.tearfund.org/Publications/F ... +Lines.htm