Name some common code smells you look for in a code review, and the refactoring that usually fixes each.

A code smell is a sign on the surface of the code that usually points to a deeper design problem. Common smells and their usual fixes:

• Long method: use Extract Method to split it into well-named steps.
• Large class or god class (one class that does too much): use Extract Class to split it by responsibility.
• Long parameter list: use Introduce Parameter Object, or pass a whole object.
• Duplicated code: use Extract Method or Pull Up Method, but only if it really is the same knowledge.
• Feature envy, a method that uses another object's data more than its own: use Move Method to move it to that object.
• Primitive obsession, such as strings for emails and numbers for money: replace the primitive with a value object.
• Shotgun surgery, where one change needs edits in many classes: use Move Method or Move Field to bring the logic together.
• Switch on type repeated in several places: use Replace Conditional with Polymorphism.

Smells are hints, not rules. Confirm the real problem before you change anything.