The sooner you get behind schedule, the more time you have to make it up.
Broad introductions to agile methods are covered elsewhere [Larman03]. In this thinking-tool chapter, there is essentially one suggestion:
‘Agile’ is not a practice. It is a quality of the organization and its people to be adaptive, responsive, continually learning and evolving—to be agile , with the goal of competitive business success and rapid delivery of economically valuable products and knowledge. One cannot do agile , although it is a common misconception ...