Under the tutelage of Dale "Deal" North, I've come to learn a thing or two about game sales over the years. Recently, Steam has started its Summer Getaway Sale, and in addition to seeing a bunch of tips flying around the net, I figured I'd impart a bit of advice -- patience is a virtue.
Rather than simply buying a game on a generic non-featured deal, it's best to actually wait and see if your game hits a Daily Deal, Flash Sale, or Community Choice to nab an even bigger savings. My personal rule is "comparison shop, then comparison shop again" -- Cheap Shark is a great site that helps categorize deals from various websites, which is key, because sites like Green Man Gaming or Amazon will often match or beat Steam Sale prices.
One last bit of advice I always give during any major Steam sale is to wait until the last day to purchase anything that hasn't hit a Daily, Flash or Community deal. At the very worst, you'll often times end up with the exact same sale price as the first couple of days.