Keep in mind that some topics are vastly under represented on the Web. Or, if represented, then the authors are sometimes suspect.

Example: A while ago, I was trying to find the answer to "What was the price of a sheet of music in 1820 Vienna?" I tried everything I could think of without success. This is true of many liberal arts topics: content in these areas is extremely spottyall of Shakespeare's works are there, in multiple editionsbut the complete works of John Donne? That's a harder question to answer.

Know the players. To be really effective on the Web, you need to know the players--what each is good at doing, and the differences in content/coverage between them. While this isn't an endorsement of these search engines, this is the kind of information I keep in my cheat sheet and find that I use quite a bit.

Keep in mind that this information changes frequently (in fact, this list will probably be out of date by the time this is printed). Make your own cheat sheet or work off mine and update frequently. Here is my current cheat sheet.