Success Secret 1#
Embrace Agile and use it correctly; don't use it as an excuse for not doing things e.g. documentation. Documentation should be produced of requirements, design and acceptance criteria, process documentation etc.
Success Secret #2
Ensure teams are co-located either physically or via IT systems and the Product Owner is part of the team. A collaboration environment which allows all team members to see requirements, development tasks, test plans and results, documentation etc all in one place is essential to success.
Success Secret #3
The team and Product Owner must be empowered to make decisions. It is all about getting decisions made quickly. Try and fail fast is the key to success.