Read source code from projects that used by wide range of people. Some tiny repository might look nice at first sight, but it could be a result of limited scope

Read source code from projects that used by wide range of people. Some tiny repository might look nice at first sight, but it could be a result of limited scope, and production codebase always involves a large range of scope. Even if there're some caveats/hacks in these codebase, it might have a valid cause and you can learn something from how it evolved or how it (dirtily or gracefully) solves the issue.