You might already know about rebates through sites like Ebates, which has been advertising pretty heavily on TV, at least in my area. If you're not familiar with rebates, it's basically money you get back when you shop through a special link. For example, if I buy a $50 shirt at Macy's and Ebates is offering 10% cash back, then I'll pay $50 and get back $5 in my Ebates account when I go to Macys.com using the link on the Ebates site.
My starting point when I want to buy something is a fabulous site called Evreward, which will tell you how much of a rebate the rebate sites are offering for a particular store, including airline miles sites. This can help you figure out which site to use for a particular purchase. However, Evreward doesn't take into account every site you might want to use. For example, I recently bought a pair of Vionic sandals at QVC, and the highest rebate offer was at Ibotta, which isn't one of the sites covered by Evreward. Therefore, you should know which sites you use that aren't part of Evreward, and remember to check those, too. Note that you shouldn't expect to receive cash back for shipping costs (it depends on the site and the store), and that some stores don't participate in any rebate sites. (Note: Amazon participates in some rebate sites, but only in very limited categories.)
Here are the rebate sites I like to use:
COUPON and PROMO CODES
Once you've identified the rebate site you'll use, take a few moments to look for a coupon code. A lot of rebate sites have a list of codes on their page for a particular store, which makes things really easy. If you don't see one there, you can always check RetailMeNot (which sometimes offers its own rebates now). Just be aware that some coupon codes can void the rebate, so you'll want to be sure you read the fine print before using a code not available on the rebate site.
Finally, look for ways to avoid paying shipping. Many sites offer free shipping if you sign up for their free rewards program. Or you might be able to score a free membership to ShopRunner, which gives you free two-day shipping at over 100 stores. Also, most stores offer free shipping with a minimum purchase, and while you don't want to spend extra money, it can sometimes be worth it to add additional items to your order, particularly if they're things you would have bought anyway (such as a similar jacket at a different store).
What's your favorite way to save while shopping online?