The way I see it you have three choices as a screenwriter. You can write simply for your own entertainment, which is indeed a very odd choice. You can write to sell or, which is a wonderful dream, or you can write to get into the business of writing professionally.
If you choose the third option you have some huge choices to make. The first one is whether you want to writer for mainstream motion pictures or whether you like the idea of being one of those maverick type independently financed filmmakers. Big decision, but not written in stone. It's one of those things that let you slide from one goal to another.
As a member of LinkedIn I answer lots of questions posed by new writers on the site. Often I've found that I am answering questions as if all of the writers want to write for the Hollywood studio world, when in reality they seem to want to make little indies. I spent my 25 years as a Hollywood literary agent so my viewpoint is always there. I've been trying to understand the mindset of someone trying to make low-budget pictures. This is hard for me.
Why would writers set their sites so low? Why would anyone want to make pictures that can only be cast with C- actors and director wannabes? People on LinkedIn post questions about packaging A list actors to their little films. What could they be thinking???????? These actors would NEVER even see their scripts, their agents and managers would never let that happen. One of my first clients was a young out-of-work actor named Kurt Russell. He had been a huge child/young-adult star that was now in the throes of no man's land. Later he once again became a huge star. I remember him telling a mutual friend that he had three stacks of screenplays on his desk. One was a stack of films that already had financing attached that would net him millions of dollars. Another one was of scripts proffered by high level relationship people and the third was a stack by the wannabe new writers that somehow got to him. He admitted that he would never read the third stack.
I guess what I'm trying to say is: why not go for the gold? If your want to do something try to make it big. Not because you will make more money (although this is quite true), but because if you get into the bigs eventually you will be able to make the movies that you want to make, and make them the way you want them.
Learn to write better, be patient, have the hero on every page, make the budget big, place the locale in a big or small US city, write in a recognizable genre, make us love the main characters, keep the plot simple and the characters complex.
If you do it right you will have those doors swing open to you. Hell, they'll send a car to pick you up.
They might not option your scripts but they will hire you to write something else. It's a wonderful experience for you.
Go the the gold......it's out there.