I de-worm my dogs once a month when I give them their heartworm medicine. It also takes care of intestinal parasites such as round, hook, and whipworm. I have never had a flea problem (knocks on wood) but I still de worm for tapeworm every 6 months. Also take in a fecal for testing once a year.
We take a "communal" (try to get a bit from each dog) specimen in at least once a year or anytime there is something suspicious. Otherwise we worm as needed, and that is rarely since we live in a climate with very few mosquitoes and almost too dry for parasites unless in confined spaces.