I don't want to go into too much detail as there is a whole book on it but the basics are:
You sow spinach [I'm using mustard] in 0.5m strips and leave it to grow
You cut this down when it gets big enough, leave it on the soil and use it to walk on.
In between, you put your crops - which are graded as As, Bs or Cs [more of that later] and you interplant them [companion planting] so that you get more than one crop from each row.
The next year, you sow your spinach where last year your crops were, and plant where your spinach was - so effectively having half your plot green manured each year whilst maximising space, and companion planting to avoid pests and diseases.
The rows are alternated as such:
A C B C A C B C
A - is crops that you only get one harvest from each year [tomatoes, peppers, squashes, runner beans etc]
B - is crops that you can sow twice in a year [beetroot, kohl rabi, dwarf French beans etc]
C - is crops where you can succession sow or get 3 or more crops from each year [Lettuce, rocket, spinach [for eating] etc].
So - my little trial plot is currently:
9 rows of mustard which is growing nicely.
The A and B rows have been sown with a mix of green manures so that they are covered with something whilst I wait patiently for the last frost to go in about 5 weeks. I'll chop this in when I plant my As and Bs out.
The Cs I am starting to sow - tonight in the first C I sowed Detroit Beetroot.
I'll take and post a photo of this first bed tomorrow, and plant out some lettuce and beets that I already have on the go.
However, the bed is already a talking point among my lottie neighbours - the neat rows of mustard make the plot look amazing and well cared for [even though other beds are still being harvested and look a little 'well worn' and one chap has gone out and bought mustard and is sowing this inbetween all his brassicas.
Video of the bed taken yesterday, 6th April 2012