I've talked before about using the principles of square foot gardening to maximize the growing potential of small areas. The quintessential bed is 4 feet by 4 feet. This size is manageable and can be tended from any side without having to step into the planting area. 4 x 8 was a better fit for our yard, but still allows me reach across from either side of the bed, assuming of course that 4x8 isn't planted up against a wall. It is really hard to reach across this 4 foot bed without trampling on something.
This was the same bed I had a bit of issues with wind and kids and clumsiness. For some reason, a bunch of the stuff did not sprout. I'm not sure if it was bad seed or birds or just the nature of gardening but it meant there were some open areas in the bed. This gave me chance to add stepping stones to help for harvesting and garden maintenance. In the remaining space I replanted what did not make an appearance before. For now though, the beets are growing and I have ample arugula and leaf lettuce.