Teeth are typically done once a year, or that's the rule of thumb I've been given. Sometimes more, sometimes less, depending on your horse's teeth. (Just like hooves the rule of thumb is like 6-8 weeks, but maybe one horse needs to be done more often and maybe another horse can get away with a little longer if not shod and it's like...wintertime when their hooves don't typically grow as fast).

Most people worm on a rotation of different wormers every other month. Your barn might already have a schedule like that. Here's an example: http://www.valleyvet.com/si_worm_facts.html