Speak your writing and record it.
Stuck? Often just talking about what it is that you have in mind, can bring a lot more ideas and developments to mind. So record what you want to communicate, then transcribe it and edit it later.
When you speak, you are spending very little conscious attention to what it is you are saying - it just comes out! This is an easy and brilliant way to defeat your “squelcher” and get you started expressing. You can get on a roll immediately!