Here is a really helpful cheat sheet infographic for using Google advanced search commands.
One of the best tricks listed here is The Minus Dot Com Trick. Place a minus sign in front of the word .com then search. Like this:
Results: The dot coms go away leaving you with more non-commercial trustworthy sources of information!
This infographic was found Chapter 14 of any of the Search Word Pro book marketing or business marketing titles.