While that advice is a decent starting point; i.e. first look to foreign key fields used frequently in joins to place indexes on.

However, beware putting indexes on any field (foreign key or otherwise) that is not particularly selective (a low rate of repetitive data). Having an index on any field that has very few distinct values will not help any query and will likely hurt update and insert performance on the same table, as inserts and updates to another index are now necessary.

HTH a bit,

Jay