According to a 2013 Strategy&/Katzenbach Center survey of global senior executives on culture and change management, the success rate of major change initiatives is only 54 percent.
I doubt that this figure has changed much over the last year or so. It certainly is consistent with what change leaders tell me now about their organisational change success rates.
This useful article in strategy+business shares 10 principles that the authors suggest should be applied to improve the success rate.
Hope you find some useful ideas in it.