That's where I start. Rarely do I have a complete idea where I'm heading when I start writing. As we all know every story, article or written piece of any kind starts with the Opening Line. The Opening Line, has the most important job of the entire piece. It must draw the reader in, and make them want to see what the next line is, and the next, and so forth. Soon, they've read the whole story, and you've captured someone's attention and hopefully their imagination for a while. If we're really lucky they don't forget us or the story.
I usually think of some short sentence. and usually there is a natural progression from it. I rarely know what it is. It must come naturally. Like Ice Cream and kids, thunder and lighting, and many other things that just seem to fit together naturally. If one has to force the next line, they weren't met to be. Consider making the next line the opening line and see if you can build from that. If that don't work, then one must start all over with a whole new opening line.
After you write a paragraph , or better yet a page or two go back and read it, if possible wait a while before you read it, see if it still grabs you and makes you want to read the rest of you project, Hopefully if you still like the opening line, others will enough that their intrigued enough to read the rest, of the story.