Just a quick one today (oooh matron)... I read a lot of scripts where the craft might be good, but at its heart the premise feels "half-baked". For whatever reason, the seed of the story at its heart feels under-developed and as a result, undermines the whole screenplay.
When I ask writers *what* their story is, this often seems to be the issue... They haven't really IDENTIFIED what *makes* it "what it is". For example, a "fish out of water story" (as in the case of many comedies); a "David and Goliath" story (some Horrors, Thrillers and dramas, legal or otherwise) or a story of "Good vs evil" (pretty much any story you care to mention). In other words, they haven't thought about it at grass roots level.
Instead, those writers may put everything onto their character's motivation or goal. This is of course a good start, but without knowing exactly *what* your story is, you may not put across *why* your character wants something or is behaving the way s/he does.
My advice to writers struggling with "half-baked" ideas is this: don't just think about what your character WANTS, think about WHY you are writing the story. You may find this holds the key to "unlocking" many of those elements - especially tone and plot - you were struggling with.