Check your Library/Application Support/Adobe/Common/Plug-ins/Media core directories for 3Rd party plug-ins. Copy them from CS6 to CC or create an alias.
Check your Documents/Adobe/After Effects CS6 folder. Copy the contents to CC or create an alias. Pre-sets done.
If you can't see the root Library file in Finder try using the Go To Folder link from the Go menu in finder and enter /Library
That should do it for most things.
Rick's suggestion regarding an alias is what I use for plug-ins, animation presets, and scripts.
Preferences don't transfer from one version to the next (though we're working on that).