Please write a list of tasks that a copy constructor and assignment operator need to do in C++ to keep exception safety, avoid memory leaks etc.
First be sure you really need to support copy. Most of the time it is not the case, and thus disabling both is the way to go.
Sometimes, you'll still need to provide duplication on a class from a polymorphic hierarchy, in that case: disable the assignment operator, write a (protected?) copy constructor, and provide a virtual clone() function.
Otherwise, in the case you are writing a value class, you're back into the land of the Orthogonal Canonical Form of Coplien. If you have a member that can't be trivially copied, you'll need to provide a copy-constructor, a destructor, an assignment-operator and a default constructor. This rule can be refined, see for instance: The Law of The Big Two
I'd also recommend to have a look at C++ FAQ regarding assignment operators, and at the copy-and-swap idiom and at GOTW.