I have two patches. The main one operates on a four-year rotation plan, the smaller one on a three-year rotation.
In the main patch, I have twelve long beds. Seven are 15 m long, the other five are 12 m long. All are about 1 m wide. As I rotate, I have to accept that the years I am growing brassicas, say, in the 12 m beds, I will not be able to grow as many cabbages as when they are in the 15 m beds. We eat an awful lot of brassicas and members of the allium family, as will be seen below.
Three are given over to brasiccas
Three to solanaceae and legumes
Three to the allium family
Three to cucurbits and roots (parsnips, carrots, beetroot and celeriac)
Each year, I rotate to the next three beds, so it doesn't matter how I decide to vary the proportions of my plants as they will not be grown in the same bed till they have rotated several times. The roots bed runs directly next to the alliums in a bid to deter carrot fly. Each year, the roots also rotate into the first of the three beds given over to the alliums. So far (six years), I have not suffered from carrot fly, but that may just be good luck.
In areas of bed left empty for long enough, I often grow members of the legume family as a kind of croppable green manure, but I do make sure that I don't grow two crops of legume without at least one intervening crop of some other type.
The smaller patch benefits from a bit of protection from wind, so I tend to use it for vegetables that stay in the ground for cropping the following spring.
Here I have 21 beds of around 3 m long by 1 m wide. They are divided into three groups of seven, one for the alliums, one for the brassicas and one for the legumes. However, the only set of beds given over solely to these particular families is the one for brassicas. I overwinter garlic and onions in four of the beds, the other three this year I will be giving over to overwintering fennel, beetroot and radiccio. During the summer, I also use the legume and allium beds for tall veg (climbing beans and sweetcorn), or slightly more delicate plants (peppers and chillis).
Edited to add: lettuce go in all over the place! Plus I grow spinach in the winter vegetable patch.