Start your search initially with only a few search terms on your topic. You can use boolean connectors to connect the terms: AND, OR and NOT.
Example:
canada and environment
Use quotes to search for phrases:
"oil sands" and alberta
Use an asterisk at the end of the root of a word to find multiple endings:
canad* will find Canada, Canada's, Canadian, Canadians
Example: canad* and "border control"