I think the most important is to slice your big projects into milestones and only the next milestone to actionable steps that you know you can do. Actionable means that you can do the thing that is written as a todo item. It's not actionable when you cannot do it but have to guess how to do it (sounds like a milestone to me).
The other most important :) thing is that you choose big projects and milestones in a way that you know you can do them if you try really hard. They sould not be too easy (boring) and unreachable to you in the moment.
Trash your hundreds of parallel projects and keep a handful of them that matters you most. Check periodically how you're making progress with them. You'll find that you don't make progress in lots of them. Maybe they're not so important to you. Learn to feel and identify this, maybe they're important to someone else. It's imperative to find the root causes why you don't do something. It gives you the control (and the feeling of control) back because you can start to solve the root case. Never skip this step.
I hope you can start with these. Remember, it's about getting to know yourself and your feelings that drive you.