First of all, this is great!
You've already been boiling down scenes and dialogue and sifting out the good stuff in your scripting process. You're always editing to an extent, but now you've got something tangible - a stack of pages or a screen full of words.
This is a representation of all of your hard work - blood, sweat and fears. Now it's time to tear it apart and break it down so you can rebuild it again. Smarter, faster, stronger. Your initial instinct isn't always the best choice for the story and this is your chance to try and find more direct ways to do and say the things you want to communicate through your characters and scenes.
It's not always fun, but this is how you get better.
TAKE SOME TIME.
The excitement as the ideas fly from the mind to the page is the reason we do what we do. Whether it's in a notebook, an outline or the actual script itself, you're fully charged and buzzing with excitement as you visualize your characters and settings. Their tone of voice, the smells in the air...
It's GENIUS! Sure to win every award!
Take a couple of days off and revisit the script. You can break this down however you want - issue by issue, the entire series, chapters, etc. Find what works for you. Sometimes I prefer to do issues when I'm writing a comic series and other times I like to wait until I've scripted the entire story. I'm all over the place - don't try to figure me out!
Taking that break is crucial to having the space you need to be objective about what you wrote and to make sure you're really reading it - not just skimming because it's fresh in your mind.
SLICE IT UP.
When you go back you're sure to notice some inconsistencies. Things that may not make sense or that don't fit the proper tone, etc. I'm particularly bad for writing wordy dialogue, but that's ok - it's a draft! I know on my next pass I'll be able to feel where the pacing is off, shorten up conversations, etc. That's part of the job. Plus, I think it's always better to have more to cut and pick what you like versus not having enough meat on the bones to work with.
CHOP CHOP CHOP.
Emotionally, this can go any number of ways. There's the excitement of finding a better way to build a scene, or even rearranging scenes to improve the narrative's flow. There's also the zombie-like stare that occurs when you think, "oh, shit - how am I going to fix this?" Depression can set in when you feel you have a mountain of work in front of you, but breaking it down into segments or following a trail of changes can make it seem less daunting.
When working on the edits for the first issue of "WHITE OF LIES", the follow up to "BLACK OF HEART", I had a similar experience. I felt sure that it was all crap and that I had no business writing at all. Mental state and other outside factors can drive this home, but my recommendation in these situations is to set your script down for another two days before coming back. The wheels weren't turning on my first attempt at editing the first issue, but on the second try it all came so quickly I could hardly write fast enough and walked away with momentum and confidence.
A NOTE ON PROCESS: Do what works best for you. As a creature of habit, I like to print out the script and go through it with a red pen. I've found it easier to concentrate on the page and keep track of my notes. It also separates the task of editing and rewriting. Once I'm done, I'll open my script and SAVE AS "Rev 2" (or whatever lingo you prefer) and move the old copy to another folder to try and keep things organized and easier to find if I need to go back to the original script.
OBSERVE YOUR CHARACTERS.
Are they well defined? Do they seem to be acting/reacting how you expected, or are they taking on a life of their own? Are they too similar to other characters in the story? Are they named Mary, Murray and Mickey?
Are there too many characters? Not enough?
Ask yourself these questions and take note of how you feel about them. Ideally I think you want your characters to take on a life of their own beyond any pre-work you may have done. BUT - if you find that they're encroaching on the space of other characters, you may have some decisions to make. Two angry old men, for example, may feel redundant in a world with a spectrum of character types. That is, unless your story is called "Two Angry Old Men", in which case, the reader knows what they're getting into ahead of time. In cases like this, you can try eliminating one character, adjusting the focus of one character (or even his age) or combining them into the same character. There are any number of options - this is more or less to focus your awareness of character observation in the world you've created.
What do your characters want and how are you conveying that to the reader? What fears are they facing or outright avoiding? Keeping these questions in mind will help you to mold your character and fine tune your story during the editing process.
I'm lumping in dialogue here too. Does it fit with the character(s)? The time period? Does it sound authentic or forced? Is there too much exposition?
Reading aloud is a good test, but I honestly hate that. Listen to your instincts and try not to tell the whole story front and center. Try and find ways to including something symbolic about the theme for your character's story arc. For example, a young woman that can't see something glaringly obvious that's happening in her life rides a horse with blinders over its eyes.
OBSERVE YOUR SCENES.
What happens? Does each scene give the reader more knowledge or character development? How is the pacing? Is it too long? Too short?
Once you've worked out those answers, broaden the scope and see how the scenes flow into one another. Is it literally your main character going from place to place meeting the other characters in the story? YAWN. If it's all exposition, you'll lose your audience fast. Pack in some action, romance, intrigue, etc. Transitions should feel organic and you can use your protagonists dialogue to help hem those seams.
What about the setting? Are you learning about your character because he or she is telling someone about the time they stopped a runaway train, or are we seeing them do it? A conversation about grizzly bears is more intense when there's one around the corner. A conversation about anything is more intense with a grizzly around the corner.
The key is finding balance across your script. Play with a change and see how it feels. When I'm stuck on a branching scene, I like to make little side-by-side outlines to intuit how each may play out and go with what feels right. If it's still not working, I go back and try it again!
Rearranging scenes can also help - just be sure you're diligent in cleaning up any other changes the redirection may have caused.
THINK ABOUT YOUR AUDIENCE.
What type of book are you writing?
I'm a firm believer in writing for yourself, but there are still some guidelines to abide by to make sure you keep your story on the rails and produce something that people will actually want to read - hopefully for money.
There's nothing wrong with mixing genres, but try to keep it to two or three tops. I would categorize "BLACK OF HEART" as a Noir Horror Thriller. Horror and Thriller already kind of go together. You could replace Thriller with Mystery and it's still pretty accurate, but throw Comedy in there and we may have a problem. And no, I don't want to read your Sci-Fi Samurai Torture Porn script. I will karate chop it to the ground.