Screenwriting : Finding a manager/agent for feature script by Zak Mir

You're asking the wrong question. You write a top-o-the-line, worthy of production script and flash it around a little bit and Agents/Managers will find you They got script snuffin' radar that won't quit.

A great script will get a manager interested, but they'll also look at the whole body of work. And they will want to get to know you a little to see if you're someone they want to work with, before ever committing to repping you. Forget about an agent - they're mostly salesmen, and new writers rarely have anything to sell (not even that "awesome" script you've worked on for years).

So, write a lot, network, and query professionally. In time, you'll make it!