Lessons are everywhere if you're willing to look for them, even in other people's complete and utter failure.
I have a special love for terrible movies. It started in college when I was introduced to "Troll 2," a terrible atrocity of a movie with wooden acting, child-like special effects, and a nonsensical plot about vegetarian goblins that turn people into plants to eat them. There is not a single troll in "Troll 2." It was just so entertainingly bad I fell in love. Ever since then I've been trolling the bottom of IMDB's rating list.
"The Room" is the subject of the Golden Globe-winning film, "The Disaster Artist." Many consider it to be the worst film ever made. Me? I think it's a work of genius. The director/producer/writer/star, Tommy Wiseau, has become a myth among bad movie aficionados. The man is a genius.
Still, as a writer, I try to find lessons where I can find them and "The Room" and "The Disaster Artist" are fertile with nuggets of writerly wisdom. Here's are a few of the lessons I learned from the general horribleness.
#1: Avoid Unnecessary Dialogue
"Oh hi Mark!" Dialogue in fiction should not be a direct reflection of the way people speak in real life. Each line should serve a purpose (characterization, moving the plot forward, producing conflict, etc.). Any superfluous dialogue should be cut in revision. There shouldn't be repeated greetings or characters repeating the same information over and over again ("I don't love Johnny anymore" x infinity).
#2: Continuity is Important
You can't introduce a completely new character during the climax of your story. You also can't introduce a breast cancer story arc that is never resolved. If you introduce a gun in the first act, that gun has to go off by the end of Act III. That's why I keep a "Bible" for each story to keep all the details straight. This is also a great job for your test readers. By the end, everything should be wrapped up in a nice, neat bow.
#3: Character Motivations Need to Make Sense
There's nothing that shatters the world of a story faster than characters behaving in illogical and unrealistic ways or when characters make decisions that no logical human being would ever make (I'm looking at you, Walking Dead). That's why you can't have two characters being cool with some random man-child showing up right before they're about to have sex or have a character laugh after hearing a story about domestic abuse or have a bunch of characters play football in an alley while wearing tuxes. Whether your characters are human, aliens, minotaurs, or whatever, the things they do need to make sense.
#4: Never Give Up on Your Dreams
If "The Disaster Artist" is about anything it's about two friends following their dreams. Even though Tommy didn't look like a typical movie star, even though he didn't speak a language that anyone could understand, even though he didn't understand basic human emotions, he still followed his dream of starring, directing, writing, and producing his own movie even though he wasn't qualified to do any of those things. Writing is the same game. You absorb rejection after rejection until you hear that sweet, sweet YES. If Tommy can do it, anyone can do it. All you need is six million dollars to burn.
Oh, and editing. Editing is important. Seriously, who the hell edited that piece of shit? Oh, it was Tommy? Gotcha. Now it makes sense.