If you plan a large piece of work, it will be good to produce an outline of the work you need to do and share it with potential contributors. Your roadmap should cover your goal and vision and include a timeline for tasks that need to be completed, thus helping new contributors to your project to get an understanding of what is currently happening on the project and what’s coming next. A roadmap is also a great tool to highlight dependencies among tasks, helping you to schedule work on them efficiently.
Milestones can be really helpful to reach your main goal. They can be organised around your project goals, dates, events, or timeframes. If you work on GitHub, you can use GitHub’s Project board to manage tasks and issues.