Editor's note: As a special bonus to TheStreet.com readers, we will be running an updated version of Jim Cramer's "Twenty-Five Rules of Investing," from his latest book, Real Money: Sane Investing in an Insane World. Here's Rule 22.

Few rules have saved me more than the 30-day preannouncement rule.

When

Tibco Software

(TIBX)

preannounces a bad quarter, do you rush to buy it? Are you someone who put money to work in

Waters

(WAT) - Get Report

right after its

vicious preannouncement in spring 2005?

If you are, this rule is for you:

Always wait 30 days after an earnings preannouncement before you buy.

I designed it because I recognize how compelling some of these price adjustments are, but they often are

not deep enough

to make the stocks ultimately attractive.

Here's why. When a company preannounces a bad quarter, it isn't just looking at the past. It is looking at its order book, its future. Believe me, if there were any hope that the company wouldn't have to preannounce -- hope in the form that maybe something could get

better

, not

worse

in the next 30 days -- the company would wait.

Preannouncements signal

ongoing

weakness. That's why I like to wait 30 days to see if anything has gotten better before I pull the trigger to buy.

Sure, I will miss some great opportunities. Most of the time, though, after 30 days, I find that there is more woe and another leg down! If there isn't, then I might miss a point or even 2, but I will be on terra firma. That's the only thing you want to be stepping on in any market, including this one.

At the time of publication, Cramer held no positions in stocks mentioned. Jim Cramer is a director and co-founder of TheStreet.com. He contributes daily market commentary for TheStreet.com's sites and serves as an adviser to the company's CEO. Outside contributing columnists for TheStreet.com and RealMoney.com, including Cramer, may, from time to time, write about stocks in which they have a position. In such cases, appropriate disclosure is made. To see his personal portfolio and find out what trades Cramer will make before he makes them, sign up for

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