It would be easy to sit there and fiddle with it, changing bits here and there in the hope that it all suddenly came together, but the reality is sometimes you have to take it apart, deconstruct and then rebuild, to discover what's wrong and to move it forward. I have a second draft at the moment which I reread the other day and have since come to the conclusion it would really benefit with being deconstructed. I could have tried to rewrite it like normal, but as it's such a great story I felt the extra effort of deconstructing it is a worthwhile effort.
By deconstruction I don't mean you should completely rewrite a screenplay from scratch, that would be terribly time-consuming and unnecessary. What I suggest is you separate each act, look closely at how it's constructed and rejig it if necessary. Yes, it is a little more work than simply going over and over your screenplay, again and again, rewriting the hell out of it, but it's worth it. So how do you go about it?
As I said above split your screenplay into acts, further splitting Act Two in half. It's far easier looking at a screenplay in smaller sections than it is as a whole.
Start with Act One and take a close look at where the beats occur. Are they in the right place? Are they strong enough? Then look at your characters. Are they appealing? Have you set them up sufficiently? Then look at your scenes. Are you getting in late and getting out early? Is there enough conflict?
The most common mistake I find in the first act, something I'm guilty of too with every single one of my first drafts, is that by spending so much time setting things up the act overruns by five to ten pages. Are there character bits you can use later in the script? Is there too much dialogue and exposition? Once you've looked at these things, rebuilt and rewritten, your first act will be in a much better place.
Then all you have to do is repeat this for the remaining three sections of your screenplay and you'll be laughing.
Sometimes it's necessary to revisit your original thinking, as your view on things will most likely have changed after you've written a few drafts. Deconstructing you screenplay is the best and most effective way to do this.