Making money in the stock market typically involves "buying low and selling high." That means buying stocks you think are undervalued, with the expectation that they'll rise.

Of course, the higher you set your desired sell price, the greater your potential profits ... but the higher your risk that you won't earn those profits.

But there's one strategy that can enable you to "buy low and sell higher" without taking on extra risk.

Here's how it works
Suppose you own 100 shares of Walgreen (NYSE: WAG). It's a relatively stable company, so you don't expect it to collapse overnight. You wouldn't sell at current prices, but with a P/E of 19, you don't exactly expect shares to be a quick double or triple. However, if Walgreen rose from its current price of $44 per share to $50, you'd consider the stock fairly valued, and you'd be willing to sell.

You can use an options strategy known as writing covered calls to increase your effective sell price. When you write a call, another investor pays you money upfront for the right to purchase your shares by a certain date at a certain price. In this case, you could receive $1.20 per share for the promise to sell Walgreen, should it reach $17.50 by Jan. 20, 2012.

Let's say Walgreen rises above $50 by Jan. 20. Your shares would be "called away" from you at your target sell price of $50. But because of your $1.20 calls, your effective sell price was $51.20, an additional 2.7% income on your $44 investment -- earned in seven months.

Should Jan. 20 roll around and Walgreen doesn't crack $50, you get to keep your shares, keep the 2.7% you earned on your calls, and, if you'd like, write new calls.

The downside
Writing covered calls allows you to earn higher returns without having to take on extra risk. Of course, it's still possible your stock could fall in value, but if you write covered calls on stocks you're comfortable owning anyway, that's a risk you were already taking, and the call premium will help to cushion your downside.

The big drawback to writing covered calls is opportunity cost. Should Walgreen soar to $70, instead of capturing the upside had you simply owned the stock, you'd be locked into your effective sell price of $51.20. But if you were planning on selling at $50 anyway, that might not be a big deal to you.

For these reasons, despite the huge premium that highfliers might earn you -- in many cases, easily 7% in just a few months -- you generally wouldn't write a covered call on such high-risk, high-reward stocks, because you'd be capping your upside while remaining exposed on the downside.

Five stocks for higher returns
What's the ideal stock for writing covered calls to raise your effective sell price? It will belong to a reasonably stable company (to protect your downside), but you won't expect it to soar overnight (so you won't miss out on a huge upside, should you be forced to sell).

Frequently, this means we're talking about stocks that may be somewhat -- though not drastically -- undervalued. Finally, since options premiums are generally higher for more volatile stocks, the strategy can be more lucrative with stable companies that still have moderately high betas.

With those criteria in mind, here are some candidates for writing covered calls to earn higher returns:

Company

P/E

Beta

Suncor Energy (NYSE: SU) 15 1.6
Xerox (NYSE: XRX) 16 1.7
Boeing (NYSE: BA) 17 1.3

Data from Motley Fool CAPS.

Make sure you're ready to sell
Writing covered calls to boost your effective sale price is a reliable strategy, especially when used on strong stocks selling at reasonable prices. And in down and sideways markets, covered call income can smooth out and pad your returns. Just make sure you're ready to sell a stock if it gets called away on you.

Writing covered calls is just one of the techniques we're using to boost returns while managing risk at Motley Fool Options. If you'd like to find out more and receive a free copy of our Options Insider playbook, simply enter your email address in the box below.

This article was originally published June 22, 2010. It has been updated.

Fool editor Ilan Moscovitz doesn't own shares of any company mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy..