Non-fiction e-books that educate your potential audience on specific topics like finance, online marketing, and business are going to make you more money than fiction books. Of course, there are always exceptions and you could write the next Harry Potter book, but if you want to create some residual income opportunities quickly, I would suggest you go for what sells first!
Apple maintains it’s viral appeal, with the iPhone X through their launch of the "Selfies on iPhone X" campaign. The secret to this example of viral marketing (which has clocked up over millions views both online and offline) is very simple: a product so great that it turns people into fans of the brand all on its own. People love themselves. If they have the possibility of spreading this love digitally through selfies, it’s almost a guaranteed win. The iPhone X’s brilliant selfie feature spread virally through various media forms before apple repurposed the viral content into one masterpiece, the iPhone X selfies film. As one of the YouTube comments says, “It’s the most beautiful thing I’ve ever seen”… This viral marketing through video has allowed Apple to spread key features such as their Portrait Lighting effects and their TrueDepth camera.