While Google seems quite smart, it cannot actually think. Google will only look for the exact terms you use in your search. Before searching, ask yourself, "Is this the best keyword for what I'm looking for? Are there synonyms or alternate ways of searching for the same thing?"
To search a phrase, put your term in "quotations": E.g., "Global Warming"
To search for synonyms, use a ~ before a word/phrase: E.g., ~global will look for "global" as well as "world", "international", etc.
To eliminate unwanted words, use a - before the word you want to eliminate from your results: E.g., -pollution
Here's an example of how this all works together:
Be specific! Think 'housing market crash 2007' v. 'economy'
Search by title: E.g., intitle:pollution ensures that the term 'pollution' is in the title of the site. Additionally, allintitle:global warming pollution ensures that EACH term shows up in the title.