I would just pick a popular library in your language of choice. It'll probably have some great code and some rough edges. It's okay. Learn how to get shit done

I would just pick a popular library in your language of choice. It'll probably have some great code and some rough edges. It's okay. Learn how to get shit done and learn elegance, too. Or you could pick a common theme and look at various implementations of it. Look at twitter api libraries and see how they differ, perhaps?