My wife hates to write. Unfortunately she's an astronomer, and scientists live by the words "publish or perish" as much as writers do. I recently gave her a piece of advice that's helped her overcome that initial resistance to get started.
Just write. It doesn't matter if it's crap, just write.
Nobody has to see the first thing you put down on paper. It can be disorganized, hackneyed, with poor grammar and atrocious spelling. It doesn't even have to be in compelete sentences. Some writers call this the "zero draft", the draft that will never see the light of day. It's the framework on which to build your first draft. The first draft is the one that looks remotely like a finished product, the one that you show your critique circle.
Starting a zero draft is easy. Just start writing the first thoughts that come into your head. It doesn't matter if the material belongs in the middle or even the end of the final product; the important thing is that you're getting words down on paper. So get started on your zero draft. Don't worry about quality at this stage. Nobody's watching.