Here are four quick tips that could help you narrow down your search to exactly what you're looking for.
#1 Quoth the raven, 'Nevermore'The Raven, I'm afraid) can be a huge help in narrowing search results. Putting quotation marks before and after two or more words will return results containing that exact phrase.
For instance, putting quotation marks around quoth the raven will return results with those exact words in that exact order.
#2 Take away the minus
If you're looking for, say, information on diabetes, the kind with Type I and Type II, and you keep getting hits with "insipidous" in them, use the dash.
A dash before a word will eliminate pages with that word. So your search would be "diabetes-insipidous."
So use a dash. It's like word-math!
#3 The dots have it
So, you need the number of skin infections between 1920 and 1940. Use the ol' double-dot trick.
Two periods, placed between two numbers, tell the search engine to use the numbers as a range, like this:
skin infections 1920..1940
Now, all that said, please know that today's search engines are just terrific at presenting what you're looking for. Sure, Google is probably most accurate, but Bing and Yahoo! aren't far behind.