Spotlight is a very good app for finding and searching files. It forms the core of my work flow. Every so often the spotlight index gets a bit confused. It has duplicate results or it doesn’t find the results you want. The problem with this is the index that records every file and folder. By deleting the index, spotlight will be forced to rebuild the index, thus solving the majority, if not all of the problems when searching.
You can view the video below, or on Youtube. Its a quick video, you simply drag the Macintosh HD drive into the privacy folder within System Preferences and then drag it back out again.