Google Scholar has a character limit for your search string and these tips will reduce the amount of characters needed to communicate the same information to the search engine.
Google Scholar interprets spaces as the AND Boolean operator (tip originated from Wichor Bramer). Example: Searching cancer AND treatment is equivalent to searching cancer treatment.
Google Scholar interprets the | symbol as the OR Boolean operator (tip originated from Wichor Bramer). Example: Searching cancer OR "malignant neoplasm" is equivalent to searching cancer|"malignant neoplasm" (note that there are no spaces around the | symbol).
Google Scholar interprets the dash as the NOT Boolean operator. Example: Searching for cancer NOT lung is equivalent to searching cancer -lung.
Google Scholar (GS) is designed to retrieve scholarly literature (which often includes peer reviewed literature), so you must add grey lit keywords to use it for this purpose. For example: [insert your search terms without the square brackets] dissertation|thesis|report and be sure to include all keywords for the types of grey literature you want to find. Read above about using Boolean Operators in Google to understand the use of the | symbol.
If you have found information on your topic on the web from, for example, a government or nonprofit website, you may use Google Advanced Search to search that website with the power of Google.