As with any research you are doing, it is important to regularly back up your Zotero library. To do so:
1. Open Zotero in Firefox or Standalone.
2. From the "Action" menu (gear icon), select "Preferences."
3. Select the "Advanced" tab and click the button "Show Data Directory."
4. Your data directory should now open up. Minimize the data directory.
5. Close Firefox or Zotero Standalone.
6. From the data driectory, copy the zotero.sqlite file and, if it appears, the 'storage' file into a new data location, such as a USB key.
To restore your Zotero library from a backup, follow these steps:
1. Go into your Data Directory (see steps 1-3 in the box to the left).
2. Close Firefox or Zotero Standalone.
3. Move the zotero.sqlite file and, if it appears, the "storage" file, into a temporary folder on your desktop.
4. Copy the zotero.sqlite file and, if it appears, the "storage" file, from your backup into the data directory.
5. Open Firefox or Zotero Standalone to ensure that your Zotero library has been restored. You can then delete the temporary folder on your desktop.