Pick your beginnings and endings well
I'm not talking some "Story" idea of jumping into the middle of the action to start the film off with a bang, although it's often a terrific idea to grab an audience as firmly and quickly as possible. But look at the greater scope of the story you want to tell. Your ultimate beginning and end provide the framework on which everything else will hang, so make sure you choose the right ones.
Do you begin with your character already in crisis, or do you need to demonstrate who they are so who they become is more apparent? Does it give the audience more satisfaction to see the character come through their trials, or to leave them teetering on the brink of a failure they've made themselves?
Be visual and audial
There HAS to be a reason this is a film and not a book. Even if you're adapting your own best-seller, make sure you tie everything to the sense of sight.
Everything you smell and feel, everything that hits your gut, comes from sight and sound. The Grimms were masters at having the words jump right off the page and into your gut with concise, evocative descriptions. Try reading the story called "Jorinda and Joringle" and tell me you're not haunted by the plaintive cry of Joringle's love as she ceases to be a girl, transformed into a bird, and lost to him - for the sin of passing too close to a witch's house at nightfall because they are too wrapped up in each other to notice the time.
Or tell me you don't feel a thrill of joy at the image of stars falling to earth as golden dollars, into the cold snow at the feet of a homeless child dressed in rags.
You can take us into any world you want if you just tell us about it. That means you have to be able to put us there, which means you have to be able to travel there yourself.
Whether you're creating somewhere new or re-creating somewhere down the block, close your eyes and stand there in your mind. What does it smell like? What do you hear? Is it cold or warm?
Then you'll have no trouble communicating clues to us to get us there too, whether it's the high school you hated or a world where a pin, a needle, a rooster and a duck stop for the night at an inn with the intention of having everything and paying for nothing.
Don't waste anything, ever. Don't include a single line, a single word that's not important. Don't include a character unless they have purpose and substance. It's better to strip away everything you don't care intimately about than have an iota of apathy anywhere in your script.
And don't cheat the audience. Jerk them around, trick them, mislead them, but don't plant threads you don't follow, and don't don't don't cheat them out of catharsis. This means that you HAVE TO know how to end a piece. The audience will forgive a shaky or long-winded beginning if they are satisfied at the end.
Endings are the hardest part of any script, no matter what they'll tell you about the trials of the second act. They're the hardest to film and the easiest to second-guess. But if you know where your character is going, physically or mentally, no one will quibble with you, and your audience will breathe a sigh of relief that they've been in the hands of a master as they leave the theatre.
And that is, after all, what you really want, isn't it? If you satisfy the needs of the story, there's no question raised about whether you "sold out" or "talked down" to your audience. There's only good storytelling, and for that you can learn a lot from the Brothers Grimm.