We’ve discussed the rise of native advertising, benefits of social media, and tips for mobile advertising, but we haven’t talked about quality viral ads. The term viral suggests a phenomenon—not a disease—though both are widespread and persistent.

What makes these advertisements so infectious? Here are some strategic marketing guidelines to consider and the memorable campaigns that used them to become famous.

Be Truthful. Everywhere you look, ads are populated with stunningly thin models. Dove flipped this trend on its head with its Campaign for Real Beauty beginning in 2004. Soap, Dove’s mainstay, took a backseat as curvy women starred in TV spots and on billboards across the country. The campaign highlighted authenticity over hyper-edited images, and people took notice. Dove aligned itself with body-positive values and sold some soap—a nice bonus.

Be Gutsy. Budweiser knows whassup. Specifically, it’s their ad campaign. The catchphrase “Whassup?” became a wink-wink-nudge-nudge household greeting after the beer company aired the spot during the 2000 Super Bowl. This was such a departure from their image that executives worried about brand damage. However, the risk paid off, winning awards and generating buzz.

Tell a Story. The Dos Equis brand of beer wanted to be more interesting. It also wanted to draw consumers, specifically young men, without intimidating them. The solution: The Most Interesting Man in the World, an older, accomplished gentleman who happens to drink Dos Equis. His adventures captivated the nation and the world because they told a story, and he became one of the most popular memes out there—an advertiser’s dream. Currently, he’s “sketching, skiing, solving, and sneaking” around the interwebs, uttering his legendary catchphrase during his downtime.

Be Memorable. Sex appeal. Surprising transitions. Witty dialogue. Old Spice’s The Man Your Man Could Smell Like is not easily forgettable. A muscular man emerges from a shower and addresses the ladies. Suddenly he’s on a boat and he has tickets for that thing you like, but no—they’re jewels. Now he’s on a horse. This ad tickles the fancy and engages both men and women, but the product is secondary to the sheer entertainment of the campaign.

If you’re lucky, your ad might become a meme and consumers will immortalize it in popular culture. If not, at least you caught the public’s attention and stayed true to your brand.