From wisebrother.com:
1. Hyphen searches. If you put a hyphen in front of a word, it excludes results with that word. The example Google gives is the phrase "jaguar speed," followed by a hyphen and the word "car". ("jaguar speed -car") So, how fast the animal is, not the car.
2. Tildes. They're the wavy dash thing. If you put one in front of a word, it also searches for synonyms of that word. So something like "music classes" . . . with a tilde in front of "classes" . . . will also look for music "lessons" and music "coaching.
3. Searching specific sites. Start with the word "site", then a colon, and the URL for the site you want to search. (For example, "site:olympics.com figure skating")
4. Searching for different file types. There's a dedicated "image search" button, but you can also specifically search for things like PDFs and MP3s. Just start your search with "filetype", followed by a colon. ("filetype:")
5. Asterisks. If you don't know a word, put an asterisk in there. It's useful if you don't know the name of a song but know SOME of the lyrics. For example, "falling down like [asterisk] into [asterisk]" is vague. But Google knows you probably mean "like pieces into place" from the Taylor Swift song "All Too Well".