How do you protect your intellectual property when you're about to write a screenplay? Is there any particular step you can take in order to make sure that the intellectual property stays firmly in your hand and that the people you pitch the idea to don't get to just steal it without properly compensating you for your efforts?
In addition to copyright, the Writers Guild has a registration system for registering scripts, treatments, synopses and outlines. Among other things, the guild agrees to have someone show up in court to give evidence as to the date a document was deposited. Their registration carries weight in the film industry since there are many cross-guild/union agreements that can constrain actions.
It is not an alternative to copyright - please register it with the U.S. Copyright office.
Someone writing a screenplay is the author of the work under copyright law by operation of law. Ideally, you should have a footer or header that contains your name, the circle c symbol, and the year it is written. Once it is complete, the copyright can be registered with the registrar of copyrights in Washington D.C. which is part of the Library of Congress.
Sometimes a screenplay will give rise to potentially trademarked spinoff products and you may want to identify potential trademarks in the course of writing it, to also seek to protect, although you will need some idea of what kinds of good or services would be sold with the trademarks sought.
Other best practices are to decline to review or accept unpublished draft screenplays or stories from other authors who can claim that you stole their ideas, to document your drafts in a time stamped manner that can be proven to a third-party, and to consult an attorney before signing any licensing or intellectual property transfer documents or contracts.
With great difficulty, if at all.
There is a somewhat well-known phenomenon called twin films, where two very similar films are released at approximately the same time; for instance, one famous case of this was the case of the Disney film A Bug's Life, and the Dreamworks film Antz, which were both released in 1998. If even big companies like them can't stop each other from stealing their ideas, it'd probably be even more difficult for an independent creator to prevent others from also doing so.
This is consequence of the fact that copyright doesn't cover ideas, it covers specific implementations of them. If you show someone a script for a movie about an ant worker going on an adventure to save the hive, there's nothing stopping someone you show it to from going off to write their own screenplay about a movie where an ant worker goes on an adventure to save the hive, as long as they don't copy any of the content of your script.
If you are outside the U.S. when the work of art is created, in most countries, you are the copyright owner by the creation of the art.
Now of course, you want to get some proof that you actually created the work of art, but nowadays it’s fairly easy to get digital files time stamped once you upload your work to web storage.
It is also important to remember that copyrights are almost exactly what they sound: They are, in general, meant as legal protection from reproduction, and they are less effective as means to protect the rather abstract of its subject.
For example, the computer executable instructions as components of an invention may manifest in an infinite number of forms to effectuate the same result, each of which may be the subject of copyright in most jurisdictions by a software engineer coding it, but unless they are, as considered under the law and precedent, close enough to each other, they will not allow for a claim to their potentially different authors.
It can be therefore a good idea to keep all the drafts, and alternative versions as they offer additional breadth to the scope one may claim.