First, recognise that there is a hell of a lot you don’t know. Next, accept that most of what you do know you will find out later is wrong. Then figure out what you can do with what you are confident you do know and be prepared to change that as you find out your knowledge was flawed, or the plan isn’t work as expected. That is how you make a dynamic plan.
Do not be afraid to begin to plan, knowing that you don’t know. Just accept that the plan will change as you learn and experience more.