Above all, avoid googling for really expensive things.

That time where all the ads I got for months were ads for ridiculously expensive servers, after I had (out of curiosity) googled for "what is the most expensive server you can buy on ebay?"

Or the time when all I got was ads for military-grade cables and connectors for months, after having googled (out of curiosity) for something or another about submarines -- most likely something about the dud submarines that the UK had sold to the Canadian government.