Know what's on the
Advanced search page for Google.
The "define:" command works but the results suck so you're probably better off using dictionary.com for word definitions if you need any precision.
But with the relatively weak search operators offered by Google it's really about figuring out the best words and phrases to search and letting the algorithms (where Google excels) do their thing.
Otherwise, I'd say the key is understanding the difference between word and phrase searches and the benefits and perils of exclusionary operators.
If Google would just add proximity operators, then search string tweaking would be much more powerful.