Lua and C++: separation of duties

Question

Please help to classify ways of organizing C++/Lua game code and to separate their duties. What are the most convenient ways, which one do you use?

For example, Lua can

Answer 1

Start small. Allow access to game entities so that you can perform map/level-specific scripting. Behaviour that is consistent across maps/levels probably doesn't need scripting.

Also, only give access to the public interface of your objects.