Select a large piece of blank paper. Buzan recommends paper be at least A4 sized or larger, and unlined to encourage use of the paper in every direction, without a predetermined structure.
Write your initial subject in the center of the paper. Buzan recommends drawing an image representing the topic. The image should be colorful, large, and without a border or boundary. By not including a boundary, you encourage branches to go off in any direction.
Write Basic Ordering Ideas around the main theme. These BOI's are similar to chapter headings in a book. They should be short, written in printed capital letters, and connected to the main image by a curved line. This line should be thicker closer to the central theme.
Write more refined sub-concepts around each BOI. These subsequent levels can be related to the BOI in a variety of ways, and do not have to be uniform. Write the concepts in printed lowercase letters, and link them to the original BOI. As before, the connecting lines should be thicker closer to the BOI, and thinner closer to the sub-concept.
Add sub-levels as you brainstorm, until you reach individual facts. Do not be concerned about structure. Mind maps are meant to grow organically.