Now you have a clear summary of everything you know about the story, and a list of specific questions that you still need to figure out.
What you need to do next is go through the questions one by one, and try to figure out the answers. This process mostly involves just thinking, brainstorming and listing possible alternatives, and trying to make the story make sense.
Here are some strategies that will help you out.
If you're struggling to come up with more creative ideas or fill in the plot holes - use the creative strategies outlined in the course. Take ideas from your favorite stories for inspiration, make lists of possible alternatives. Then pick your favorite answer. Try to reverse/exaggerate your ideas, try to make unusual metaphors and associations. Browse inspiring images, lists of movies, and Wikipedia articles.
If you're struggling to find an answer to a question - try to make your question as specific as possible. The more precise you get, the more clearly you define and describe your problem, the easier it will be to figure out the answer. Before looking for the answer, try to describe and discuss the problem from all angles, list all the things relevant to the question that you already know.
You can also try to describe the opposite of what you're trying to accomplish, what's definitely not going to happen next. Explain why you don't like this answer, and it will help you to figure out the answer you do like.
Yet another approach is to list the examples of the kind of thing you're looking for. Not the interesting high-quality answers you actually want, just a few things you might see in a similar story, or use to explain your question to a friend.
Very often you'll find that one of these examples is the answer you were looking for, or something you can turn into the answer by building on top of it.
Don't criticize your answers. Your first goal is to find any acceptable answer that makes any sense at all, you can improve upon it later.
Above all - keep things simple and be obvious. At this point you have already created an interesting story with a lot of fun and creative ideas, you don't need all your answers to be mind-blowing. If you can think of the most straightforward, predictable, obvious answer - just use it, it will work perfectly fine.
Usually by this point I have managed to figure out the answers to most of the questions, but I'm still having trouble with some of the remaining ones.
Now, the best strategy to use is to talk to other people, more often than not they will help you to find the answers and give you a lot of ideas you didn't think of.
If you have a friend with similar interests - talking to them is a good place to start. If that still doesn't help - it's time to make a post in our #creating-adventures channel, and tap into the power of Reddit's hivemind - make posts in /r/DMAcademy and /r/DndAdventureWriter and ask people to help.
When making a post:
Following these guidelines will greatly increase your chances of receiving useful feedback. Also, you will often notice that just going through the process of writing a high quality question helps you to figure out the answer on your own.
After requesting help on Discord and Reddit and following this advice, you're very likely to have most of your problems resolved.
If that still hasn't happened - just omit whatever parts of the story are causing you trouble, and go with the simpler version. It's likely that some of your ideas will come up during the playtest and will be solved with the help of the players.
You can also always go back to your adventure when you have more experience, and see if you can find an answer then.