Writing

It helps a lot if you have some kind of record, either in hard copy or electronic, that establishes that YOU wrote those words.

Generally speaking, if you are published by any kind of legitimate publisher, they actually take care of the silly details. I have had exactly one mainstream publication, nearly 20 years ago, and the copyright, while obtained by the outfit that published, is in my name. Not that anyone is very likely to want to plagiarize my little story, or use it in some other form. It's of course a fantasy of mine that someone would stumble across it and (smacking forehead with palm) say OMG! This is brilliant! I want to republish/make a movie/create a TV show. Alas, I doubt that will ever happen.