The blunt, unadorned truth is that your story is unlikely to be made into a movie, and not because it's not fantastic, just because movies are very different beasts and what goes into making a good movie isn't often what makes a good book. I am telling you this blunt, unadorned truth to help you manage your own expectations.
It's tempting to finish there and just say, 'Good luck with that!' but I feel an explanation - or even just some information - may be in order. So here are the Things to Know About Turning Books into Movies.
1. Adapting novels into screenplays is very difficult. If you work off the principle that each page of a screenplay is one minute of screen time, and that a film will average 90 minutes, that's a 90-page screenplay. And screenplays are not like books: there is lots of white space on each page. So your 300-page novel has to be turned into a 90-page screenplay that contains very little description and mostly dialogue, which means a lot of the story has to go. And it has to be a certain type of story to withstand that kind of stripping down. Usually a story with a good, clear dramatic arc and strong protagonists. No arc? Fahgeddaboutit.
2. It's important to remember that, as the author of the 300-page novel, you are not likely to be the person best qualified to write the 90-page screenplay adaptation of your novel, unless you have screenwriting experience. And, at any rate, seeing your novel turned into a screenplay is a bit like watching sausages get made: not advisable, especially for vegetarians.
3. One of the major factors - if not the major factor - that goes into deciding whether or not a book is suitable for adaptation to screen is how much it would cost to make as a movie. If your book is set in the past or the future, that complicates matters. Vintage cars, clothes and locations cost money; so do spaceships. Any producer who is thinking about adapting your novel is going to primarily ponder the cost of making the movie or series that results.
4. It helps if your book has sold well, if only to get it to the attention of producers. There are so many books out there - the producers need to have a reason to read yours, and a built-in readership-cum-audience is a persuasive reason. Of course, having a great story helps too ...
5. You thought the publishing industry was slow? We are sprinters compared to the cross-country game of the film industry. So even if your story is getting some attention amongst film types, prepare to wait, and wait, and wait, for anything to happen. First you'll wait for the option to be done. Then you'll wait for a screenwriter to be attached. Then you'll wait for the screenplay to go through development, while the producer drums up funds. And on it goes.
6. This last point is an important one for those of you who don't have access to an agent or lawyer: do not straightaway sell your film or TV rights. Not to the first person who asks, nor to the last. If someone wants to turn your book into a movie, they have to option the material. And that is an option to purchase. They get to buy the rights when they plug in the lights on the first day of filming.
So while I don't like to encourage writers to give up on their dreams, in this particular area it is advisable to keep the dreams at a manageable level. But, then again, I'm not of the school of telling people to just 'dream big!!!' anyway, mainly because I have seen what disappointment looks like and I'd rather spare you all that experience. As the sole cause of disappointment is expectation, better to manage your expectations.