1. Get good writers.

2. Get good directors.

3. Get good actors.

It's not simply a matter of getting good people. They've gotten good people in the past and turned them away.

And there are other things to consider -

At this point the story of Iron Man is pretty much told. Where do you go from there? - Can the Avengers series carry on without Tony Stark or will they keep jamming him awkwardly into other films ala Nick Fury?

if they keep branching out with new characters then things will probably be fine but I'm not sure how things will pan out if they keep forcing an Avengers 'reunion' every few years.

4. Don't sh*t on the fanbase and if possible get them on your side by staying true to the source.

I guess we saw an example of this with the Mandarin. Although I am fairly certain that a lot of the people complaining had never heard of the character before.

I actually liked what they did there with Trevor Slattery.