Object Calisthenics outlines 9 basic rules to apply when performing the exercise:
- One level of indentation per method.
- Don't use the ELSE keyword.
- Wrap all primitives and Strings in classes.
- First class collections.
- One dot per line.
- Don't abbreviate.
- Keep all classes less than 50 lines.
- No classes with more than two instance variables.
- No getters or setters.
Also see the "Your code sucks, let's fix-it" presentation by Rafael Dohms.