How can i motivate myself to write a book?

I’ve never written anything before, but I had what i consider to be a sweet idea for a novel. I Wrote like one paragraph but I still haven’t decided whats going on further down the road. I know I need to construct the plot, but other than just thinking about it occasionally I can’t seem to get the ball rolling. I don’t know if i just subconsciously know it will suck. Or maybe I’m just procrastinating. Any ideas on motivation or experience with writing?