How do I add friends, Pages, groups, events or apps back to my News Feed after I hide them?

From your home page:

1. Hover over the News Feed bookmark in the left column
2. Click the icon that appears to the left and select Edit Settings
3. Click X next to the name of the friend, Page, group, event or app whose stories you want to unhide
4. Click Save

Removing someone or something from your list of hidden stories means those stories can appear in your News Feed again.