Last week, Twitter’s Claire Diaz-Ortiz, the company’s leader for social innovation, released her book all about how people can use Twitter to be good global citizens. But the book, Twitter for Good, is only one part of Twitter’s focus on social change: Hope140, Twitter’s web site for supporting causes, serves as a launch pad for the various ways social media can make a positive difference. Here are the top 5 things Hope140 is doing right at this juncture. 1. Listing specific causes. Right on its front page, Hope140 lists three big, broad causes that you can support: #hope4japan for earthquake relief, International Literacy Day, and Help Haiti Now. Even if these causes don’t speak to you, or are evolving faster than Twitter updates the Hope140 web site, listing specific causes helps give people ideas about the ways we can make an impact through Twitter. Furthermore, literacy and disaster relief are two huge categories — proving that though tweets are small, the differences we can make are big.