Two of my favorite tricks for online shopping:
1) Retail Me Not. Before I check out anywhere, I always google "_____ (name of the store) promo code." Nearly every time I do this, RetailMeNot has a nifty little coupon code that will knock 20% of my total order, give me free shipping, or otherwise make me feel smart and thrifty!
2) Amazon Prime. Worth it. My family all shares one account. We get free streaming TV and movies and we get free two-day shipping. This makes Amazon the most cost-effective place to shop almost always. Again, before I click the "check out" button on any other site, I do a quick check to see if I can find it on Amazon, for cheaper and with free shipping. Usually, I can.
My last piece of advice is not really a trick, but a mantra: You CAN find what you are looking for. It's the INTERNET, it's out there. You just have to know what to look for and be determined enough to find it. And you will.
And that's how to win at online shopping.