Congrats on the film! First, keep in mind that everyone has a different story about getting representation. (Please feel free to share yours in the comments!) Some writers have absolutely no credits, get an agent, and then sell something (or get staffed). Other people do it in the opposite order because agents often look for people who have already gotten their first job/sale/etc. Agents want people who are ready to make money. If there's a random script floating around, an agent isn't going to want to represent the writer unless people agree that he or she has a lot of talent. But if you make a sale, I think more agents will come running. You'll have "heat." I know it's frustrating, since many companies won't consider your material until you already have representation...but this is why making personal connections is so important.
Managers, in my experience, are more likely to take on clients with less experience or heat. People who have talent but need a little work. I've blogged a little about this before, in terms of why you might have better luck querying managers than querying agents. Many writers first get managers, work on their material and then get agents when they're ready to go out into the marketplace and sell stuff or get staffed. Managers can help you get an agent, or vice versa, if you find yourself in the opposite position.
Some writers only have agents, and not managers...but once you're a pro, it's rare to have just a manager and not an agent. Generally, managers help you develop your material, connect you with producers and directors, etc. Agents do the selling. At each agency, agents are assigned to cover specific studios and networks and report back on what work is available at each place. Managers usually have fewer clients, and spend more time on each client. They also sometimes produce their clients' material (agents can't). The duties of managers and agents definitely do overlap; it's not as though agents can't read your stuff and give you notes, or that managers won't know what's selling in the marketplace. Both can get you meetings. It's not that one is "better" than the other, just different.
Back to Michael: It sounds like you are ready to look for an agent, especially if you've written a few other scripts. It certainly won't hurt that you have a film being shot in Australia, but how impressed people will be by that will vary. Some agents specialize in foreign talent, so you might want to do some research and find them. You can write queries if you like, but I have blogged before about why they're mostly a waste of time. I would try to use any LA connections you have, or ask the Australian people producing your film if they have any connections here. Assuming you didn't direct the film and want to get an agent to further your career as a director, you don't really need to wait until the film is released. For writers, it's the script that will function as your sample, not the movie.
