Start writing, no matter what. The water does not flow until the faucet is turned on.
However many holy words you read, however many you speak, what good will they do you if you do not act on them?
This is how you do it: you sit down at the keyboard and you put one word after another until its done. It's that easy, and that hard.
To believe in something, and not to live it, is dishonest.