If you are an investor doing homework for a portfolio of stocks, Jim Cramer warns that your homework may be incomplete, or worse, it may full of mistakes.

A huge part of success in picking stocks is determining where they are headed. Likewise, to appropriately anticipate direction, proper homework is key.

It is common knowledge that most of the time, stocks trade on its earnings-per-share number. However, Cramer warned against watching only that figure.

"You need to be aware that for some industries, earnings are not the most important metric, and if the only thing you're watching is the earnings per share, you could end up getting clobbered or missing some fabulous opportunities," he said.

For example, when dealing with an oil company, production growth is important. With a tech company, the average selling price of a product is a telling sign of a healthy stock. In these two sectors, both of these metrics have significantly more weight than anything relating to earnings estimates.

For instance, Cramer's charitable trust owned Devon Energy during a time when it consistently beat earnings estimates.

A winner, right? Wrong. The company's production growth disappointed quarter after quarter. Ultimately, Devon just wasn't producing enough new oil and the stock fell on production shortfalls. So, even though it technically beat Wall Street's estimates, the measure of production growth was more important.

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The issue of critical metrics works both ways. Meaning, that a positive key metric can power a stock higher when many other metrics appear negative.

The lesson here is quite simple: Investors must be aware of all the critical metrics specific to a stock.

There simply is no cookie cutter way to conduct research. It must be specific to the stock and its industry, so that important red flags and potential opportunities both garner attention.

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