So the question is, what aspect of writing do you want to learn or practice? If you're looking at actual word choice, you can't learn that from a book (unless you need to improve your basic grammar). For that kind of thing you need to produce pages of script and get critique on them. But if you want to study any of the deeper aspects, there are a variety of books I could recommend depending on what particular aspect you want to study.
Grammar I've got down, and I think I do alright when it comes to writing _A_ conversation. Stringing those conversations together to keep an arc going, particularly when the main character is transitioning from one sub-plot to the next, is where I have trouble: To my ears those conversations sound either contrived or not 'real' in some way.
I'm using a 2D engine, which limits the visual cues I can give, though I try to work with what I've got: reading from a bookshelf, examining a spot mentioned by an NPC, a temple divided on the inside to show the divide of religions in the town. I can't hang Chekov's Gun on a wall, though.
I don't have the book anymore, so I can't give an exact quote, but in the opening of The Chronicles of Thomas Covenant, the Unbeliever, Thomas is asked by a 'man', "If you found yourself in a world you knew to be not real, would you fight to save it, anyway? That is the heart of morality." The main character (Sofia) who has lived her whole life in a small mining town in the mountains (Pleroma), releases a Bad Thing into the world. Finding no help in the village, she (with her companions) then descends into the world to warn them.
No one will hear her voice: they cling to prophecies, the stability of government, and religious institutions, each of which successively fails and falls.
Act I, "The Failure of Men" is primarily 'limited by geography'. You travel from region to region: a bridge, a mountain pass, a boat (which opens up some choice), until you find yourself at the 'heart' of the continent. The big battle ensues, the good guys lose, the 'hero' is killed, and you end up fleeing for your life while the world around you is being consumed by evil.
Enter Act 2, "The Search for Truth", where you find out that everything you thought you knew has been completely twisted (The 'big bad' didn't start out that way). In fact most of the people here are more than ok with your home continent being destroyed. While these people trust in 'the truth', Sofia's words fall on deaf ears. The Truth fails to offer any protection, and this land, too is destroyed.
Cue Act 3, "Just Us". In Zulu (starring a young Michael Caine), a frightened soldier asks the color sergeant, "Why? Why is it us?" "Because we're here, lad; and nobody else. Just us." The only thing that hasn't failed is you. And so you start your personal battle and the long voyage home.
I've got the timeline for Act 1 done, and the key conversations scripted - but those are like snapshots. Filling in the spaces is where I falter. I'm drawing a lot of inspiration from the Xenosaga Trilogy (a cinematic game if ever there was one) as well as "The Pistis Sophia", and trying to stay away from the Baldur's Gate, Star Wars, Sword of Shanarra script (or at least the obvious appearance of that script) as much as I can.
I hope somewhere in there I managed to get something across that you can use to point me in a good direction. Maybe this is a case of "I don't know what I don't know." I do know something is missing in the details though. Yes, they have to cross the mountain to meet the king in denial while his lands rot around him, but I need a more convincing reason than 'You've done all there is to do on this side', or worse 'You've outleveled all the critters in this area, please proceed to the next hub to resume grinding XP', and 'Go to the next monarch on your list' seems to fall rather flat: the initial premise being that no king will risk acting alone, but if you can convince enough of them...
I'm reading 'The Writer's Journey' by Christopher Vogler (the story of the hero and the archetypes along the way).and she's given me Worlds of Wonder and a complete Fantasy Reference. I just went in to see if she had anything else I should mention and I found a little book ('Elements of Fiction Writing') on Scene and Structure she'd been holding out on me