If you haven't already used it up during a credit card splurge around Amazon Prime Day, then you ought to take the opportunity to sign up for a free 30-day trial of Amazon Prime. That will get you early access to the Lightning Deals, and help you grab some of Jeff's best deals of the day. It will also net you free shipping on a host of products and speedy delivery too, and at the very worst it'll be handy when it comes to bagging some last-minute Christmas gifts for that aunt you always forget about.
The other trick is to use CamelCamelCamel to find out the general pricing trend of the product you're after. Sometimes sellers can try and trick you into thinking a deal is better than it really is, and that means hiking up the price beforehand for a 'bigger' discount on the day.