Investing may be serious business, but having a little fun with it could actually benefit your portfolio.

In a recent issue of our Motley Fool Rule Breakers newsletter, Fool co-founder David Gardner pointed out that it's important to enjoy following the companies in which we invest. If it's a chore to read your holdings' annual and quarterly reports, or follow their latest news, you just won't do a good job of it.

Who are you?
David asked investors: "What do you love? Who are you? What do you want from this world?" Those key questions can help you zero in on the companies that may serve you best.

Some businesses clearly seem more fun than others: Activision Blizzard (Nasdaq: ATVI), for example, is in the fast-paced video game business, while Campbell Soup (NYSE: CPB) makes, uh, soup (among other things). But for some people, even soup can be fun to follow.

The Ethisphere Institute also recently named Campbell Soup one of the World's Most Ethical Companies for 2010 -- along with several dozen others, including Adobe (Nasdaq: ABDE) and National Grid (NYSE: NGG). That sort of news could easily get fans of socially responsible businesses fired up.

Other investors might enjoy watching companies cater to Americans' greater interest in healthful fare. PepsiCo (NYSE: PEP) and Kraft (NYSE: KFT) are just the latest big food companies announcing plans to reduce the sodium in their offerings. If you really believe in what these businesses are doing, you'll likely want to keep up with their progress.

Just don't forget about price
While you definitely want companies you'll enjoy following, you also need to buy them at attractive prices. For a rough idea of whether a given stock is a bargain, compare its current P/E ratio or price-to-sales ratio with those metrics' historic ranges. If a company's current number is 16, and it's swung between 12 and 36 over the past few years, it would seem relatively inexpensive. 

Seek good values and good fun in your investments. Your portfolio might thank you for it.

What kinds of companies are most fun for you to follow? Let us know in the comment box below.

Attention, Fools! Looking for a trustworthy financial planner? The Garrett Planning Network is offering a limited-time 10% discount for new Motley Fool clients. Just click this link, search your state, and look for the Motley Fool icon to identify participating advisors.

Adobe Systems and Activision Blizzard are Motley Fool Stock Advisor picks. National Grid and PepsiCo are Motley Fool Income Investor recommendations. Motley Fool Options has recommended a synthetic long position on Activision Blizzard and a diagonal call position on PepsiCo. The Fool owns shares of Activision Blizzard. Try any of our investing newsletter services free for 30 days.

Longtime Fool contributor Selena Maranjian owns shares of PepsiCo and Activision Blizzard, and cans of Campbell's soups. Given the chance, Andy Warhol would have totally done a painting of the Fool's disclosure policy.