Check out this excellent article by the always excellent Lucy V. Hay. Right on the money. I’d add three things, if you’re writing the report for your own benefit, to improve your writing.
1 – Genre – did the script do anything for you emotionally (which is what genre is all about)? Did it make you laugh, shudder, etc?
2 – How did the writer get away with it? All scripts have to get over crucial issues, whether it’s a potential plot hole or a challenging theme. How did he/she do it?
3. (And this is the big-headed one) How would you have done it differently? Might have been better, might have been worse. Maybe you’d have ducked a big challenge (and can learn from that) or maybe you’d have tried to stick out for a darker ending…
Oh, one last thing, don’t just read good scripts, read bad ones too!! Most producers read too many bad scripts and don’t realise how good a screenplay can be, but most writers (if they read scripts at all) read only the good ones.
They don’t realise just how bad most scripts are. If they did, they’d work much harder at getting their own work sold and made. Go do some reading.