Practice is important for building the skills required to be a productive TDD developer. You must master new technical skills such as dependency injection, MVC/MVVM, unit-testing frameworks, and supporting frameworks such as NBehave. You also must make many mental adjustments when approaching TDD, such as adopting the SOLID Principles and becoming comfortable with the idea of test-first development.
For the purposes of creating a TDD kata, this appendix provides a series of user stories for the OSIM application. This application is sparse and incomplete by design. My hope is that you will take these user stories and complete the OSIM as a form of kata. Do it once. Then do it again. Then do it again. Keep doing it until you are comfortable with your TDD skills. This is especially necessary if you are not currently working in an environment that supports TDD. Your skill is like a saw. It could be made by the best craftsman using the finest materials, but if you do not maintain it, it will not stay sharp for long.