Another option for adding a lot of items to Zotero at once is to import references saved in a .ris file. RIS is a standard file format for structured citation data; Zotero reads the file and converts it into citations.
To import RIS files:
This is the most labor-intensive way to enter references into Zotero, but sometimes it's the only option. Especially if there is no readily available record for your item online.
If you're using Zotero Standalone, you need to install the browser plug-in for your browser of choice.
The Zotero web translator lets you harvest citation information (metadata) from databases and websites with one click. Simply navigate to the item and click the Add to Zotero button () to harvest the record.
Keep in mind:
If you know the standard identifier for the item you're working with (DOI, PubMed ID, or ISBN), Zotero can harvest other relevant bibliographic information using that identifer.
If you've already got a lot of sources saved on your computer, it can be a pain to locate online records to harvest citation information for Zotero. Luckily, Zotero can automatically extract metadata from many* PDF files.
*For this to work, the PDF quality must be good enough for Zotero to extract identifying text information and a matching record for the article must exist in Google Scholar. Zotero harvests Google Scholar metadata to create the item record.