2. Commit to researching
Take the dollar amount of an item you want to purchase and spend that number in minutes researching the product. So, if it's a $60 keyboard, spend 60 minutes digging up information. (Take this with a grain of salt--you certainly don't need to spend 25 hours researching a $1,500 TV.)
Read customer reviews (especially the bad ones), expert reviews, search for comparable products, and ask friends if they've had any experience with the product or Web site. Use services like Decide and Google Shopping to find out if now is the best time to purchase the item and if there's a better price out there.
Do this for any product. I mean it--a blouse, universal remote, phone case, anything. By the time you finish doing so, you might find a cheaper price, better product, or realize you no longer want it.