I think a key part is simple: good story quality. Key steps:
- Eliminate duplicates. The submission system should quickly warn of potentially duplicate URLs or subject words.
- Quick review. Find a way to have a quick review of the story summary before posting. You don't want to slow down the flow too much, but it'd be good to have someone check for missing "not"s, URLs that don't work, and so on. I would assume you already have a spelling and grammar checker, but it's not clear it's always working. That sort of basic for a few sentences really shouldn't take that long.
- Try to find good topics. That one in some sense is the hardest.
The discussions are sometimes interesting - and sometimes not. But I think if the stories start higher-quality, the follow-up discussion is more likely to be better.
In the longer term, the system for entering text is... quirky. Has someone considered using Markdown? Yeah, Markdown processors vary, but lots of people know Markdown (e.g., via GitHub), and specs like CommonMark and libraries like Red Carpet make it fairly painless.