It's always tempting to test out your story idea by pitching or sending a query before the novel or script is finished. Not a good idea. What if your query is accepted and the agent/publisher/studio loves the query and wants to read a partial or the full? You have just blown your contact. That's it, that was your first and only chance to make an impression.
Why? Because the agent (I'm just going to use agent from here out, to simplify) doesn't want to see your partial in one month, three months or a year, he wants to see it now. So what if he's going to take weeks or months to get back to you? That's his end of the business. Your end of the business is to be professional and send him a finished manuscript/script ASAP, while you are still fresh in his mind.
This may sound stupid, but you wouldn't apply for a job/career as a nurse without first getting your BS in Nursing. In any other field, you'd get an education, do your internship, and get some experience before applying for a job. And I'm talking about a professional job here, not flipping burgers (which I actually do for a living, as the owner of course). So why would you just flipantly jot off a query to an agent without actually having something to show them? And doing some research into your market?
So, you have your manuscript/script finished, can you query now? NO!!! If you haven't polished your pages to within an inch of life, you aren't ready to offer up your words to a professional. Writing is rewriting, and you have to rewrite, polish, put the damn thing away for a time, then come back with a fresh eye and start polishing again.
When you think you have done everything possible to make your words sparkle, and jump off the page, then it's time to write that query. And not a moment sooner!