The United States Institute of Peace has a very interesting paper out on ‘Democratic Breakthroughs: the Ingredients of Successful Revolts.’ It's a bit reductionist, but identifies some potentially informative patterns. This from the summary:
The cases of successful breakthrough examined in this study are the Soviet Union in 1991 and Russia in 1993, Poland in 1989, Serbia in 2000, Ukraine in 2004, Indonesia by 1999, Chile in 1988, and South Africa by 1996. Cases of failed and then ultimately successful democratic transition are Ghana by 2000, Mexico by 2000, South Korea by 1987, and Turkey by 1983. Finally, the cases of failed transition examined are Algeria in 1991, Iran in 1979, China in 1989, and Azerbaijan in 2005.