...Or experiment yourself first, then use the information on this site, Cognos support and other web communities that host discussions like this.
Simply put, BI =
Database (Data Warehouse) ---> Metadata Modeling ---> Reporting
...regardless of the toolset you pick. If modeling best practices are what you need, then the FM user guide is probably the wrong place to be looking. This will mostly tell you how to use the product.
As mentioned up top, best practice information can be found all over these places I listed.
Books by Bill Inmon and/or Ralph Kimball would prove helpful as well.