When I decide to read a series I read all the books in the series that are available at that time. Non-stop. (Re-reads, too.)
Now, "decide to read it" will depend on a lot of factors: whether the series is open-ended, whether individual volumes are more or less self-contained, whether the author is actively working on the series and new volumes come out on a regular basis.
Some series (Wheel of Time, Song of Ice and Fire) I'll wait until the project is finished and the verdict is in that the mega-novel works. (I call it my "TWIN PEAKS" rule.)
Finished narratives I'll do in one sitting.
LORD OF THE RINGS, for example, I read back-to-back-to-back. Twice in the same week.
(I was 17 and impressionable, okay?)
Ditto for Tarzan and the bulk of the ERN canon.
(Same time period.)
Once I read PRINCESS OF MARS I scavenged every volume in print and ran through the full catalog. Took six months.
Availability factored in, of course; so I read other stuff while waiting for the mail to bring in the next load. (Plus the six years that it took me to locate a set of the APACHE DEVIL/WAR CHIEF set.) But TARZAN I read all 25 volumes in a row. A very fun month.
Let's say I'm "somewhat" persistent... okay, stubborn.
