CSS file organisation as well as the structure and workflow can turn into a big pile of unmanageable code. It usually start with a nice and clean idea how things will work and as the site grows and coding is done under time pressure you start to loose it bit by bit. Sounds familiar?
Two of the biggest problems identified in the past is that the code was either too specific or not specific enough, which caused the problems down the line. Big files full of CSS code are also quite hard to work with.
Structure
Dividing CSS into smaller reusable chunks, specially when CSS preprocessor such are SASS is used are very useful. General rule: try to divide your CSS file into small meaningful code sections and save them as separate files. Then use some form of processor which generates a single file out of them, remove spaces, comments etc. for your production.
Order your CSS