Whoever it was who set this all out before will, I'm sure, refer you to his (I think) very useful message.
An important thing to remember is continuity, or succession, or whatever you call it. You don't want 15 cauliflowers ready at the same time. But you'll always get them!! So - leave space in each row for the successive plantings. Don't start another row some distance away, or you'll run into rotation problems. On the other hand, with cabbages, for instance, winter varieties should be kept together so that the summer plot can more easily be dug over. If you get my drift?? = Tim