Organizing ideas by order of importance is a common arrangement of ideas. When you give reasons to support your point, you can decide that certain reasons have more importance than others,and then present the most important reason first to make a strong impression/and then follow it by other, less important reasons. Or you can present the less important reason first, building up to other more important reasons and finish with the most important reason so that your reader will remember it best. Both ways are effective.
The transitional signals for order of importance are somewhat similar to the listing signals you have studied in Chapter 5. But some words or phrases are added to indicate the importance of the items.