Stop thinking about it! Seriously, the key is to start. Somewhere - it doesn't matter where.
At some time, how about now? There is no later - you only got right now! Show up in the thing that you want to start and then once you are started be consistent. Keep showing up. It is quite simple... but how do we actually do it?
We got to stay accountable, starting with ourselves. Then to those around us. If we need more help with accountability you can reach out to a coach.
As long as you start, it doesn't matter if you start small or you start big. You don't have to know everything, the details will come to you as you go along. The journey reveals itself, a step a time.
Anything big can only be tackled with small efforts. When you eat your food, you take a bite at a time, you don't swallow the plate like they do in cartoons.
Can you break your big project into small projects? That way it works like a puzzle. You are still solving a big puzzle but you are only working on parts of the puzzle. With each section you complete the closer you come to completing the puzzle.
Start small and consistently on a big goal, stay accountable and the rest will be revealed. You can't see past a corner unless you reach at the corner and you turn.