What is the best steps / procedure to buy online and guarantee to have the lowest prices and best price?

There are many sites web, promotion codes, "hot deals", said one day, etc. .. online offerings do not know where to start!?! Does anyone have and tested a few steps, websites and the procedure used and have always gotten the best deals? For example, whenever I go to Froogle first, find the lower price and then I'm not going to get keycodes.com and promo codes for additional savings and free shipping coupon?

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