For example, if you are doing a history project on what it was like to be a child in Britain during World War Two, typing this into a search engine won't give you very clear reults. The extra words will only confuse the search engine:
what was it like being a child in Britain during World War Two
Instead, pick a few well-chosen key words:
children WW2 Britian
For example, if you want to find out about the human heart for some Science homework, don't simply type heart. This doesn't give the search engine enough information. Instead, you need to tell it that we only want pages that have the both the words heart and human in them, by placing a + between the words:
heart + human
For example, if you want to find information on the town Kingston Upon Thames, it is better to put speech marks around the words, so that the search engine treats it as one phrase, not 3 separate key words:
"Kingston Upon Thames"
This will stop your search results including pages from America and the rest of the world.