Here’s another simple little exercise that you might add to your arsenal:  

Before releasing your new play or screenplay to anyone for the first time and after you think you’ve made all necessary revisions and the script really works for you from beginning to end, I suggest you take your rewriting process one step further.

Put the script away for a few days, still not showing it to anyone.  When you pull it out again, get it out of the computer by printing a hard copy so you’re literally able to hold the script in your hands.  This will give you an initial degree of distance to and objectivity toward your material that you can’t ever achieve by simply charging back into it on your computer screen.  

Then, sitting there looking at the title page, try to reprogram your brain to become an ultra-sensitive scanning machine that you’re going to put each page through.  Make yourself into this hyper-critical, word sensitive, fine-tuning device that can pick up even the slightest static or doubt or nag of uncertainty.  With this machine nothing gets through that isn’t absolutely perfect.  

Then feed in the first page and begin scanning through each stage direction, description of action, and line of dialogue word by word.  When anything stops you–a word choice, the smallest whisper of “this isn’t perfect but it’s good enough” or “do I really need this?” and so on–have the beeper in your mind go off and stop and fix it.  Don’t move on until you can scan back over the same material and, in all honesty, the beeper no longer sounds.

And when you come across difficult problems that you just can’t get by the scanner no matter how hard you try, then at least you’ve discovered key issues that you may need outside help with–problem areas that can only be completely solved after you get trusted feedback from others or hear the script read by actors and/or feel how an audience responds to it.  But by faithfully going through this tough solo-testing first, at least you will have identified where and what these issues are.  You’ll be aware of what to watch and listen for, what questions to begin asking once you release your project for the first time.   
The point here is to make your script as good as it can possibly get before you put it out there for others to respond to.  That’s the only way you’re going to make genuine progress with it from here on out.  If you’re not happy with what you’re asking others to respond to or at least aren’t privately aware of where you have potential issues, why waste their time?
The simple fact is that in this scriptwriting game there’s no room for the slightest sloppiness or laziness.  Anything less than your absolute best effort just doesn’t cut it.  In the end you never get away with it.  True professionalism means more than extraordinary talent.  It means patience and hard work and being honest with yourself as to how good your writing really is.  Every writer of plays and/or screenplays who has consistent success in the profession takes this as a matter of course.  Becoming your own scanning machine (or whatever you want to call it), therefore, is simply one of the essential requirements.