Oh dear, in my very early stories (the dark past) I made the mistake of not having the overall plot written, and I got totally lost in my own story after 2 or 3 chapters, which led me to dropping the whole thing out. Thankfully it wasn't anything I published anywhere hahaha.
So I usually have at least an overall plot with beginning / middle / end + some trivia ready, and then fully constructed characters with how I want them to evolve.
As for LOTR, I think if both the story and the characters are excellent, you can't know which one drives the other haha.