Just post naturally; if you find a subject that interests you, don't limit yourself to 3 posts and call it a day.

On the other hand, if there is nothing going on that you feel like participating in, don't force yourself to; that would in a sense be spam.
This might lead you to a large variation in the number of posts on a day to day basis, but you'll definitely have more fun this way.

I can hardly imagine a scenario without atleast 3 threads that's interesting enough to find a way to contribute!