“The principle of crop rotation is to grow specific groups of vegetables on a different part of the vegetable plot each year. This helps to reduce a build-up of crop-specific pest and disease problems and it organises groups of crops according to their cultivation needs.” – RHS
This subject always sounds difficult and produces much discussion amongst new vegetable growers. However, there is plenty of advice available and with a little reading the matter becomes much more simple and less like some form of deep gardening magic.
The Royal Horticultural Society has a simple explanation and plans on its website. If you want to read more deeply on the subject then this link gives you historical background as well as detailed family groups of vegetables.
But the basic rule is not to grow the same crop in the same bed every year.