Where I work has been using Scrum for a while now but it seems to have gone through a few phases. In terms of obstacles, one part is to prevent putting in too much change at once and just introduce things slowly,e.g. put in a daily standup one week, a couple weeks later put in a story board, a couple weeks later bring in pair programming. This allows for the various tweaks that will happen to work and if the changes improve things then this can help build up some good momentum. Another point is to make sure that if there should be changes in how something is done that the person being corrected isn't belittled or mocked. At times this may mean that you interrupt someone or that you bring in a "Can we get back to basics?" or something similar to try to put things back on track rather than just yelling at someone or doing something else that is counterproductive.
Bringing in consultants was one of the best things done around here, IMO. Now, these guys came in to help evolve how development was done here. Bringing in pair programming, TDD, concepts like broken windows, organizing project folders, and bringing in mocking for tests, were all excellent additions that while we may have gotten there on our own, it may have taken a long time which wouldn't work out so well.
