What are the best practices for re-throwing exceptions in C#?

When re-throwing an exception, use the `throw;` statement (without specifying the exception object) to preserve the original stack trace. Using `throw ex;` will create a new exception instance with a new stack trace starting at the re-throw point, which makes debugging difficult. Re-throw exceptions only when you need to add additional information or perform cleanup before the exception propagates further up the call stack.