TL;DR
To start the wheels of your project, your task as a project manager is to create a project plan. Johanna’s advice is to plan in timeboxes, beginning with a short one that would enable you to start the project. This is another post from the project management series. The post is based on a remarkable book written by Johanna Rothman, Manage It!
Johanna’s advice is straightforward, start with planning just enough to get you started. This also includes zero step, create a project charter. But how to actually do that?
You first need to define your planning timebox, amount of time in which your team will deliver part of the product. Keep in mind that it is ok to iterate over project charter and plan. You need to apply Empirical planning, not Predictive planning. We all try to do predictive planning. The planning timebox is too big (several months), and we strive to predict the future. Johanna warns us that predicting the future is only possible using crystal ball (or I would like to add, using a machine created in Devs).
In empirical planning, in the beginning, we use a shorter timebox, to give a team a chance to create something. We plan the next timebox using empirical (adjective, based on, concerned with, or verifiable by observation or experience rather than theory or pure logic) information from the first timebox.
But what should plan contain? When you have a project charter, you have drivers, goals, and success criteria. You have some requirements. In your plan, you select with your team which features would be implemented at the end of the timebox. You keep in mind your drivers and do not forget about goals. Goals are features not requested by the sponsor, but from your team (e.g., use unit testing or example mapping). You keep in mind the end of the time box. What release criteria should be satisfied at the end of that timebox.
Conclusion
Plan just enough to get started.