I finished re-reading Prince Caspian earlier today. Here, based on what we've seen, are my predictions on how it has been adapted for screen. (We tend to forget that post-production now lasts longer than production, aka. filming, on these movies...)
Caspian's nurse will be cut.
I don't want it to happen, but her purpose in the story would get bogged down in a film. With them wanting to keep the appearance of characters balanced, Caspian's story will likely start with him under Dr. Cornelius' tutelage. (LEWIS NOTE: Caspian's relationship with Cornerlius was most likely based on Lewis' tutelage with Dr. Kirkpatrick.)
The Pevensies will meet Caspian before Miraz lays siege to Aslan's How.
Evidently he will be drawn to the How by a failed attempt to "capture" or "rescue" someone, said to be a dwarf. While I thought it would be Dr. Cornelius (which I still think is a good idea, Caspian going to save a friend), but it looks like it will be Trumpkin. Perhaps he is re-captured when Telmarines spot the the Pevensies on the way to the How? (The idea of an attack on Miraz's castle was probably based on Reepicheep's suggestion at Dancing Lawn.)
Anyways, there are my predictions for now.