A book turning into a series

Primarily when it comes to writing a series your first thought is not, "This book could be the start of a series."  It just doesn't really happen that way.  Generally it takes some thought --a lot of thought--and then once you've decided to turn the book into a series more ideas come into mind and etc.
With the Magicians series I didn't start writing Cursed with Power until after I had decided I was going to write a series.  I realized during the summer that the only series I had written was The Magic of Light trilogy --of course mind you that is a trilogy, as I said.  I wanted to write another series; something new and fresh that could be continued on for more than three books.  It had to be something everybody could get involved in and I wanted it to be entirely different from The Magic of Light.
In June of 2010 this year I pretty much had posted something on Write Here's blog in which I asked for everyone's opinion on the kind of series I should begin.  The options were vague: a series about the last of Dark magicians, in which each book focuses on a different Dark magician and their struggles to stay alive OR an ordinary man with a talent for archery who takes on the most bizarre of adventures.
Evidently I chose my first option because the idea fascinated me.  Dark magicians of some sort are always mentioned in fantasy books but they are rarely ever focused on.  And let's face it, when do you ever learn much about the "bad guy" in a story?  Rarely once again.

Now you've gotten to take a look into my mind for that decision.  This is how the Magicians series came about. What started out as a crazy idea during the summer turned into a series I am now more than ready to dedicate myself to.