There are jobs to be had all across the frequency spectrum.
No hard and fast rules, cause ultimately it depends on the customer, but typically your most frequent jobs are storefronts and restaurants (weekly, bi-weekly and monthly are most common), followed by commercial and residential (typically quarterly, semiannual and annual) then last is po folks residential (people who get the itch to clean up their act every few years or so).
Ideally, you should arrange some kind of recurring work with EVERY customer you can. Unless they are a big pain in the butt, then just smile, collect your check and move on.
Offering discounts for frequent cleaning is up to your discretion in a lot of ways. Don't feel like you have to. But it can be a good way to drive business and increase your yearly gross.