Jim Agnes, famous director and writer, said that when writing a movie script you need to make sure the dialogues need to be "well executed", they need to move, have beats, they shouldn't be "bogged down in minutia", they shouldn't do exposition, they should show and not tell. What does it mean exactly to be well executed?
In movie scripts, dialogue is typically sparse. You need to rely on the director and the actors to convey the emotions, the body language, the facial expressions, the tone of voice and emotions in the voice. And just as importantly, we rely on the music to set the emotional tone. Movies have musical sound tracks written by composers that are excellent at emotional manipulation of the audience by music.
Given good actors and a good musical score, a simple "No" can capture all the heartbreak of a page of text, or equally all the joy of a page of text.
Well executed means it sound natural, it is as sparse as possible without being confusing, and it is "expert" in understanding where to rely on the director, the music, and the actors to convey meaning.
Like "yes" or "no", the context in which they are uttered can be everything.
Movies are first and foremost visual storytelling. You can rely on the music (which you don't write) to convey the emotions of the moment. The more feelings and state of mind you can communicate visually, the better. Dialogue tends to be a support for when the visuals and emotional music are not enough to know what is happening.
This takes a lot of visualization.
I could say the same about fiction, although more relaxed than a screenplay. Fiction is less strict about length, screenplays are extremely strict about length. But similarly, long speeches should be nearly barred.
Pay attention, in highly rated fiction on TV and in film, to how very little is actually said, but you understand it completely because of the visuals provided by the actors and the audio emotional support.
Sometimes if you write out just the dialogue, the dialogue seems much too sparse to convey what you gather by watching it done. The context in which it is said and how it is said and the cues of the music convey most of the meaning.
Believe it or not that is well done dialogue; it is not intended to be read by itself.