I was hoping to find some beta readers for what I have so far, because I'm always in the habit of second-guessing myself, and what I have done is come up with some answers for nonexistent questions.
When I was younger, I was taught to write a story from beginning to end. That was how you did it - sequentially. That was how it was done. Imagine my relief and surprise when I began discovering real, published writers that skirted around troubling scenes with placeholders like, "this is where the fight scene will go"!
When I am struggling with a difficult passage, I always mark the place with some conversational text or the content that inspired the idea (wikipedia knowledge, links, etc.) and then I can move on to the scenes that are actually clear in my mind, dialogue and all. Often times, I'll find that those "difficult scenes" can actually be used as foreshadowing, once I've written past them enough. If I can't decide what to have two people do while they're alone in a room, I'll just jot down "they talk for a while", and keep going. Later on, though, a murder occurs. Hmm...why don't I have them pick up a paper, or turn on the TV? There's a murder trial going on.
"Wow", she said, "Imagine killing someone because they took your parking space."
He looked at her, wondering if he was imagining nervousness in her voice. "People do strange things sometimes." Why did he say that? Now she was looking at him funny!
Now I have two scenes for the price of one!
I've been jumping around in my novel a bit, trying to get all of the things I've imagined down so that I can reorder them if necessary and use them to puzzle out the missing details. It beats sitting at the end of a scene and not being able to move on!
Also, in case you're wondering, I do sometimes post before completing. With a computer and modem like I've got, stalling until you've finished all your thoughts is going to end up costing you the entire post. I've had crashes that wiped out documents I'd just saved, Internet access that conveniently decides to disconnect right before I press Post or Update, and power outages that blink on and off like someone's kicking the switch. I might even edit this post.