You have heard this repeated hundreds of times. It's like someone is banging your head on the wall for you. But, it is because there's a large amount of truth to it. Of course there are exceptions, but ultimately if you can't create an engaging push within those first ten to twelve pages then you need to rework something.
A common problem we hear with these first pages is how to gain propulsion quickly, but effectively (effectively = engaging). A lot of things need to happen in these first pages, right? Yes, but this structure can be executed in a lot of different ways. One thing to NOT do is drag out an "artistic" opening. What is this? Well, it's that influence we have in our heads that tells us to drag out action lines all throughout those first pages. You know, where our lead showers, then shaves, then gives a thousand yard stare in a mirror contemplating life. Don't do this. It's boring. It takes up valuable intro time. And it is predictable. It disengages the reader.
How can you avoid the trap door mentioned above? Sprint into your opening development. Sometimes (if you have meticulously outlined your story already) opening with a scene that will appear later down the road (a midpoint, a climax, something) can help this process. It immediately puts your audience into the perspective and actions of your protagonist (and potentially the antagonist as well), thus showing us that character vividly.
Your beginning pages are the most important of your screenplay. They draw the reader in to the character and the world they are roaming around in. Open up with precision, but engaging force. Don't adopt the lackluster attitude of boring action acting as development. That will have your script in the worse place possible: the trash can.