I'm having issues trying to create a search scope for a single document library. Do I just simply go to the scope settings in the search service application, create a new shared scope and add a new rule and paste in the document library URL?
Firstly, I think you can create search scope at SITE COLLECTION level rather at the farm level for this requirement.
If the library is new, wait for the indexing to happen.
Follow this thread , see the last response.
1st. Make sure your doc library is set to YES to Allow items to appers in search results in the Advanced Settings of the doc library.
2nd. Configure search at site collection under Site Collection Administration
Enable Custom Scopes > point this URL to your search center site collection
Search Drop Down Mode Show, and default to "s" URL parameter.