Marketingfag. Malcom Gladwell's The Tipping Point is about how to get a meme to spread.
Three key factors:
1) The Law of the Few: Many disease outbreaks can be traced to a small number of key infectors - connectors, mavens, and salespeople.
2) The Stickiness Factor: A unique quality that causes the idea to "stick" - often being dramatically divergent from conventional wisdom.
3) The Power of Context: External conditions can speed, slow, or stop a meme.
Cliff notes here are worth a quick review for memefags and twatterfags:
http:// www.wikisummaries.org/wiki/The_Tipping_Point