The reference to document number should probably be removed from the advice as the document number is an internal identifier for a document within the Funnelback index.
You can't directly control the document number assigned to a document and it will change every time the index is rebuilt.
However, low document numbers are generally assigned to documents that are discovered early during a crawl - this means that items that are in the seed list (start URLs) or linked closely from the start URLs will have low document numbers.