I've heard that before you look for an agent you need to have your script polished to perfection. Is it the same way with looking for a manager? Should you look for a manager with just one script completed or should you have a variety? Tell what you think, thanks!
If all you've got is a single diamond, however finely polished it may be, that doesn't make you a gemologist.
And managers aren't in the business of selling diamonds -- they're in the business of managing the careers of gemologist.
That requires not *one* diamond (and that presumes the monumentally unlikely proposition that the very first gem you cut and polish will, in fact, be even up to industrial grade, never mind a gem of museum quality) but a body of work that demonstrates your ability as a someone who can cut and polish gems consistently, to order, and on a timely basis.
So what I tell anybody who isn't already a professional writer in some other area (that is, unless you are already a professsional working novelist or playwright or journalist) is that if all you've done is finish one screenplay -- or if you haven't even finished one, then you shouldn't be thinking in terms of agents or managers or query letters.
You should be thinking in terms of your next script, because the chances of this first script of yours, or anyone's first script, being good enough to sell are, if not nil, then virtually nil.
And the last thing you want to do is to burn a bunch of bridges -- by which I mean potential contacts -- by sending them an unsaleable script now, when a few years from now, after gaining a lot more experience by writing a lot more screenplays, you will be in a far better position to make those contacts with some possibility of a successful outcome.
NMS