Screenwriters are not always on set, they do not have the high profiles like directors and actors, and there are a lot more people who think they can fit this role. To differentiate yourself, and actually get your work taken seriously, you will need a screenwriting agent to represent you. This person makes contacts professionally, sends your work out, and tries to either get your work sold or get you a consistent job doing the kind of writing that you have shown them you can do. The first step here is to actually get that agent, then to make them work for you.
The first thing you have to remember about screenwriting agents is they do not want to hear from you or read your scripts. They, more than any other entertainment agents or managers, have to deal with sizable inquiries that are overwhelming and the majority are not going to make it. The old assumption that everyone in Hollywood has a script is somewhat true, and you are not going to be any different to them.
Your first submission to them will never be your script because it will be sent back to you unopened in almost any case. This is because they
do not want the legal recourse of what could happen with a script they have seen but choose not to represent. Unsolicited scripts could get them sued if a film is produced with some of the elements in your script, so they will not even open it to prove that they could not have looked at it. What you want to do is to call the assistant for the screenwriting agent and ask about the submission process. If you are lucky, or if you have some connection to them personally or professionally, you will be asked to send in a query letter. This screenplay query letter will give some information about your script, such as a treatment, and possibly information about you as a writer.
If they are interested then they will request a copy of the script, which is only the first step. At this point, you send a physical copy of the script, not an email or digital file, since this will protect you in terms of having parts of the work stolen. You may even want to have the work copyrighted or registered with the WGA ahead of time, but this is not something you need to make known to the agent.
The agent may not even read the script that has come in and hire a reader, which is a person hired to read and write coverage for scripts. This reader may just present the agent with a one or two sheet outlining what the script is about and whether or not they will believe the agent will be interested in it. If they are then interested, you may be signed by that agent for representation. This clears a major hurdle but is not a guarantee you will be hired to work as a professional writer in the film or television industry. Make sure you do not make contact with the agent unless you have completed work already that you think is of a superior quality and marketable nature.
From here, you do not want to just let the screenplay agent work as the main contractor of your career, but you also do not want to overwhelm them with contact. Just as there are a lot of spec screenplays around the industry, there are a lot of signed writers in a major agency looking for work. It is important for you to continue to try to get work created, make suggestions, make contacts, and try to get your work out into the world. The screenplay agent will then add some sense of legitimacy to your work as most places will not even read it if you do not have formal representation.
The agent will then make a lot of contacts to see what is available and also inform you about what people are looking for. They can never tell you whether or not your work is going to be better one way or the other, but they can say what people are requesting and if they feel that your work is a good fit. This does not mean that you should suddenly change your style, but it allows you an insight into the industry that you desperately need.
Source: Author's own experience.