What do popular apps on the App Store do to launch so massively?

I've always wondered how the biggest apps out there, that sometimes start with little to no funding, become so huge and get so many adopters (like Snapchat). If you've been successful in that space and had to do it all over again: which platforms, strategies, forums, etc. would you launch on to get early adoption and then mass appeal? It's very hard for me to understand how to execute and get a clear path, there's just so many things to do at once, that you can become…