Public affairs professionals wondering which blogs to read and influence must think like detectives.

The natural starting point is sites like Technorati, Google Blog Search, or IceRocket, though Adfero Group MD Jeff Mascott notes that search terms must be refined, since searching the vast blogosphere is different than combing through an array of print publications.

"Using just a search term like 'education' will produce too much in the way of junk," Mascott says.

He recommends first understanding exactly what audience the public ...