Number One: Always look for coupon or promotional codes. We have dozens listed alphabetically on our Saving with 6abc Codes and Coupons page. You can Google the retailer and the word "coupon."
Once you find codes, it's time to "Stack." See if the site will accept more than one code -- or if you can use the code along with an offer like free shipping.
Number Three: sometimes, it pays to buy more to save more. If you can get 30% off a $100 purchase, but you were only planning to buy $70 worth of merchandise, see if you can find $30 worth of things you can use as gifts, or place an order with a friend and split the savings on the items that will turn out to be free.
Number Four: Use social media. If you like retailers on Facebook or follow them or Twitter, you'll have access to deals they post just for their fans.
As for the "Don'ts:" Don't be committed to specific brand -- be willing to switch to save. Don't give out any personal information until you're ready to make a purchase. Don't forget to read the fine print. And finally, Don't ever pay for coupons.