You just need to shut off the inner critic, and start writing.
There are two main approaches: pantsing, and plotting.
As I answered in the question linked above, pantsing works for very few people. Plotting is a better approach, for me at least.
Write down a rough, one page summary of what you want the book to be, create a few characters, create 30-40 scenes which move the story forward, and start writing.
As you write, you don't have to stick to the plan. If you dont like a character, just ignore them and continue writing, but don't go back to edit your novel. If you don't like the plot, again change it on the fly, and pretend that's what you wrote. You can always fix any plot holes in editing.
The dilemma you are stuck in happens to everyone, and the only way out is to type out 50-60,000 words, without criticising yourself or trying to edit. There is no easy way, you just have to slog through the process.
A way to make this easy is to write what you love. This may or may not be what you like reading, or the type of writer you want to be. For a long time I wanted to be a serious writer, the type that wins awards & stuff. But every time I tried to write such books, my muse revolted, and like you I ended up writing nothing.
Accepting that I have my own style, and it may never win me the Pulitzer award was one of the biggest challenges for me, harder than how to create a plot/character, things all the blog writers want to talk about.
I will end with a quote from Scott Berkun:
This means that when people can’t start they’re imagining the precision of the end, all polished and brilliant, a vision that makes the ugly clumsy junkyard that all beginnings are, impossible to accept. Good voice, tone, rhythm, ideas and grammar are essential to good writing, but they’re never introduced all at once.
Have you ever been blocked while playing Frisbee? Eating doughnuts? Dancing naked in your living room? Those are joyful things and there’s nothing at stake: if you fail, who cares? Nobody. If there are no rules, and no judgment, psychological blocks are impossible. And remember writers like making names and overthinking things: there is no term for architect-block, painter-block, juggler-block or composer-block. Every creative pursuit faces similar pressures, but they don’t obsess about it the way writers seem to do.