Make all C# code structures start as private as possible
Whenever I create a new item using the normal interface for such an action (for instance, right-click on a folder and click "New Class..."), that thing should start off as private as possible. New classes should be internal with a private constructor. New methods, fields, properties, and indexers should be private. People should have to do work to make something more public, not more private.
Barring that, the ability to easily edit the template used to create those things would be great.