I found this one tip hugely useful when I was writing novels:
Assume that your first draft will be crap.
It helps to know that even professional writers produce crap on their first attempt. It’s allowed to be crap. You can even sort of aim for it to be crap. It’s really really important to suspend your inner critic at the first draft stage. Your inner critic is your worst enemy at that point: your inner critic is a cruel malicious bully who you would never allow anywhere near anybody you loved.
But without that first draft, you have nothing. So: allow yourself to write utter nonsense, because no matter how crap it is, it is content. It is raw material. And you really badly need that raw material in order to proceed.
Once you have the raw material, invite your inner critic back to the party. Now you can edit and craft and hone.
Oh yes, and here’s a sub-item which I guess I learnt so long ago, I’d forgotten about it: Editing your own work is not as bad as you think.
When I was at school writing essays, I only ever wrote one draft and handed it straight in. This was because I couldn’t bear to read my own work back to myself – I always hated it. But then I realised that it was really satisfying to edit my own work, and it meant I could make it a lot better.
So, use the “rubbish first draft” to get you past that first I-don’t-want-to-do-it hurdle, because you are giving yourself permission to produce utter dross. And it doesn’t matter, because you’re going to go back and improve it – which is a really satisfying process.