There are several excellent tutorials about viral marketing on the net. To read them all is very recommend:

• Viral Marketing (A detailed introduction)

• Build a Buzz with Viral Marketing ("..Whatever you call it this week - propagation marketing, inertia marketing, contagion marketing - viral marketing is a simple but powerful way to get noticed by an ever-increasing audience...")

• The Pros of Viral Marketing (Article)

• What Makes It Viral? ("..The newest buzzword to hit e-mail marketing these days has to be "viral." Everyone wants his or her marketing message to be viral, have a viral aspect, and capitalize on viral marketing. But do people understand what it is that makes their marketing message worthy of being passed along?..")

• How to Catch on to Viral Marketing ("..Viral marketing has quickly achieved recognition because of a handful of high-profile examples: Marketers demonstrated that on shoestring budgets they could motivate millions. They did so by leveraging customer-to-customer communication to increase sales, brand awareness, and market coverage...")

• Viral Marketing With Incentives ("..As a rule, traditional marketing concepts and vehicles do not translate well online. For example...")

• Getting Viral ("..So what is viral marketing on the Internet? Simply word of mouth? No way. Word of mouth on steroids? That's more like it...")

• Viral Marketing - Subliminal Advertising ("..Think good word of mouth just happens? Positive buzz, the secret ingredient of a successful product launch, is rarely left to chance. Instead, companies are hedging their bets by recruiting online opinion leaders to ensure a warm reception for their product. This subversive campaign tactic gets results...")

• Viral Marketing: Worth Catching ("..For very little money or effort, even the smallest online businesses can use viral marketing techniques - the same techniques that helped make Amazon.com one of the largest online shopping destinations..")

• Viral Branding: Spread the Bug ("..Branding is about communicating a message about your company's values then filling those expectations, thereby building a reputation. One of the most vital mechanisms in this process is word-of-mouth, or viral, marketing...")

• Essentials of Word of Mouth Marketing ("..Every business, either knowingly or unknowingly, generates word of mouth that is either positive - which helps build their business, or negative - which hurts it. There are even some fortunate (but relatively few) businesses that rely entirely on word of mouth to generate more business than they can handle...")

• The Six Simple Principles of Viral Marketing ("..I admit it. The term "viral marketing" is offensive. Call yourself a Viral Marketer and people will take two steps back. I would...")

• Email List Viral Marketing 101 (Tutorial)

• and more...