Look for:
- code breaking "Conventions and Guidlines", both Higher-level Guidelines and Conventions
- duplicated state (variables and attributes)
- duplicated code or logic
- code that doesn't belong to a file
- value scope is too long, e.g. it's calculated early and then not used for many lines
- methods too complicated or too big
- interdependent state
- interleaved code, i.e. several aspects taking turns within a single code block