"Buy weakness. Sell strength," Jim Cramer told his

"RealMoney" radio show listeners Tuesday.

It's a mantra he repeats often, and he said it again because many people who bought stocks when prices were going up got crushed in the latest market selloff.

Commodities and their related stocks were up a tremendous amount since the beginning of the year, he said. These commodities include zinc, steel, copper, gold, silver and aluminum, along with industries like mining and companies that make earth-moving and safety products.

He said that this is all part of the commodities complex and that the complex has been soaring because developing nations of the world need these building blocks to develop their infrastructures.

Investors who bought this complex low and started scaling out last week did not get crushed by this selloff, he said. They sold into strength. "Scaling out" means selling out of a position in pieces.

But a lot of people bought into the commodities complex after it had already moved considerably higher, hoping that it would just continue to climb.

So, when these stocks took a swan dive, traders who bought them up had no choice but to panic, he said. For example, if an investor paid $102 for

Phelps Dodge

( PD) five days ago and then watched it go to $87 just a few days later, of course, panic set in.

Cramer said that the trick is not only to scale out of stocks as they grow very strong, but to also pick up stocks when people are panicking and taking the prices down.

Soon, we'll be able to start buying these stocks again in steps, he said, adding that investors who sold some of these stocks in a panic can start picking them up again now that the price is lower.

However, he warned that stocks need to be bought in increments, just as they should be sold in increments. This is because one can never be sure that a stock has bottomed, and buying in increments gives investors an opportunity to buy a little more at a lower price.

Cramer said that mid-cap tech stocks look like they may have reached a bottom, including

Rackable

(RACK)

and

National Semiconductor

(NSM)

.

Financials may soon stop falling because the

Federal Reserve

may stop raising rates now that commodities prices have collapsed, he said. In this space, he likes

Commerce Bancorp

(CBH) - Get Report

and

Countrywide Financial

( CFC), which Cramer owns for his

Action Alerts PLUS portfolio.

He believes that the retailer

Coldwater Creek

(CWTR)

is a best-of-breed company that is just marking time, and that now is the time to buy

Whole Foods

( WFMI). The company reported a great quarter, but the stock has fallen.

Moreover, he said that

Starbucks

(SBUX) - Get Report

is a buy. It also reported an unbelievable quarter, but the stock pulled back 10% overnight.

In the commodities complex, he reminded listeners that "oil has its own pulse," and that he would not be afraid to start buying some here. Specifically, he said to look at

ConocoPhillips

(COP) - Get Report

. Not only is Warren Buffett buying the stock, it's really cheap now. He also said he would look at

Marathon Oil

(MRO) - Get Report

and

Schlumberger

(SLB) - Get Report

.

To see the most recent edition of The RealMoney Radio Recap in its entirety, please click here. This recap is published every day around 3 p.m. ET.

At the time of publication, Cramer was long Commerce Bancorp and Countrywide Financial.

James J. 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

Action Alerts PLUS. While he cannot provide personalized investment advice or recommendations, he invites you to send comments on his column by

clicking here. Listen to Cramer's RealMoney Radio show on your computer; just click

here. Watch Cramer on "Mad Money" at 6 p.m. ET weeknights on CNBC. Click

here to order Cramer's latest book, "Real Money: Sane Investing in an Insane World," click

here to get his second book, "You Got Screwed!" and click

here to order Cramer's autobiography, "Confessions of a Street Addict."