Lady Courage:),
I absolutely agree. Film makers should respect Lewis, or any writers material. These particular film makers argued that the novel was too long to adapt in a 2 hour production.
But for some reason they found it logical to add more to the story (in PC and VODT) even though they argued the original material was "too long".

Dear Michael Apted-
Move over and let NarniaWebbers make VDT.

That would be amazing.

Although all of these tips are great, I would just like to add one more. I'm almost sure that this will never happen, but I feel like it needs to be said.

Don't be afraid to change actors to keep ages accurate. 11 is not 8 and never will be. Of course this is all relative, but if left go to far, you could end up like Glee with thirty year olds in highschool.

Not every movie needs a romance!

There's a lot of cool ideas many could come up with. As for giving real advice that actual film makers don't already know? I don't know.

I agree with what others have said. Find film makers who love the source material and understand it. Also, they need a visionary; someone who has a really genius idea of how it could be implemented.

Something I think would be cool for a Narnia film is the way Aslan could be portrayed. For instance, as part of the LWW extended edition DVD set, there was a documentary about C.S. Lewis, called "C.S. Lewis - Dreamer of Narnia". The opening sequence to that was really cool; mimicking the creation of Narnia with some artistic shots of a lion as well. The way they photographed the lion was really cool. It gave a very powerful and mysterious feeling to the lion. It felt a little like something from National Geographic though, but it was better than anything I've seen in any of the Narnia films. I'm assuming they used a real lion for this documentary? The lion in the documentary actually looked closer to Pauline Baynes' artwork of Aslan too I think.
So something I would like to see is more artistic cinematography and a much more majestic depiction of Aslan, since he is the one key thread between all of the stories and the main point of the series.
If there's anything people could take away from a future Narnia movie, I'd want the audience to never look at lions the same way again.

I'd say a good movie needs a good cast, good director, and a great soundtrack.