Model driven development

For big projects model driven development can be needed, but when a small project comes up it is probably better to keep paperwork minimum and delve into prototyping(assuming you have a framework to build upon). Generally a well studied use-case and activity diagrams of a few key scenarios and state diagram of a few key entities would suffice. Key to success is test driven development i believe. For me any project scope larger than 6 months is doomed to fail. Even a big project can be scheduled to give fruits in 6 months cycle.