1) Own a Hardcover book to record ideas & lyrics in as they come along. That way when you are scheduled to write you already have a bit of material ready to roll. So it takes the pressure off slightly and doesn’t feel like you’ve wasted so much time simply looking at a blank piece of paper.
Having a hardcover strangely assists as well, as you give it more respect and don’t loose it as easy as you would just a throw away exercise book.
Whenever I hear (or think I hear) something cool, I write it down in the book. As it’s all in the same place I actually do know I’ll come back to it when I’m writing. And thus the moment won’t be lost : )
2) Decide on a topic. Then brainstorm any kind of word or sentence you think of related to the topic. Write and write fast! It doesn’t matter if it’s messy or rubbish. It gives you a palate of options to work with.