Rule #1:
From now until the LAST DAY of the sale, if a game is on sale as a daily deal or flash deal, you can buy it. If it is only "on sale" through July 23, pass. Do not buy. Save your money (you may need it).

Rule #2:
Check each day for the daily deals, and monitor flash deals. As games come up that you want, you can get them. Just continue to exercise self control for games that are not a daily/flash deal.

Rule #3:
You can purchase the large packs, such as the THQ pack or Square-Enix/Eidos pack at any time if you wish. It is extremely unlikely that those bundles will be discounted any further, even though individual games in those packs may become daily deals. If you want a bundle, go for it. Lots of games, excellent price.

Rule #4:
On the LAST DAY of the sale, Steam traditionally makes its daily deals an encore of the most popular daily deals from the previous days. Go nuts. Buy everything you wanted. New games are almost never on the daily deals during the last day. At this point, it is safe to buy anything else you've been waiting on.

Rule #5:
If you miss a game from a daily deal, STILL DO NOT BUY IT until the last day. As I said, the final day often recaps previous days' daily deals, so there is still a chance the game you missed could come around as a daily deal again. Don't rush it. If it doesn't, you can still buy it at the standard sale price on the last day, and just be sad you missed the daily deal. Just remember that if you missed it on one day, it's not necessarily too late. Save money by keeping a cool head.

Steam seller:
(In case if you need someone to help you buy it because you don't have credit card or other problem)

Steam down. Looks like there's an attack going on?

Post #10 so I get a free Humble Indie #10!