When dealing with object oriented design and refactoring, it's important to consider the reasons WHY we want to make the object structures we use. The big thing is Behavior normalization and the second is data normalization and the third is something i would call interaction normalization (the interaction between the behavior of methods and the data their using). 

I was having a hard time coming up with a concise explanation why I write objects the way that I do because i've mostly just learned it by looking at other people's code in books and examples. However, i found this amazing article/essay about the topic here and it explains in 'just enough' detail what it was that i was ineffective at verbalizing.

http://www.agiledata.org/essays/classNormalization.html