If you followed my previous recommendations, then you have already put some time and thought into your story. You should be in a great position to get to actual writing! I will provide 2 suggestions for this part of the process.
First, do NOT get caught up in editing. It is really, really easy to write a chapter and then spend a lot of time reviewing it, refining it, rewriting it, etc. Do not get bogged down with that at this point. There is plenty of time later for this. You need to be focused on getting your story written. Like most everything, there is momentum when writing. Do not interrupt it with review. Just keep moving forward and churn out your chapters.
This doesn't mean you can't do any review, just be very careful. Books have stagnated and died because of this. Keep writing!!!
The other item I will recommend is probably something you already considered at an earlier point of the process, but I wanted to make mention. I read an excellent book by Orson Scott Card (Ender's Game) about book characters. Being that I find his characters to be of high quality, I paid attention. Of the many fine points, the one that really helped me, was this: No one thinks that they are the bad guy. What this means is that from a person's point of view, they rarely view themselves or their actions as bad.
For example, the movie E.T. The bad guys were the government. As a viewer, you hated them because you knew that E.T. was a nice being that just wanted to get home. However, imagine if the movie was done from the government's point of view! An alien spaceship, a possible extra-terrestrial with who-knows-what kind of powers, technology, or even disease. Fox Mulder would be all over that! Those agents were just doing their job as scientists and protectors. Not bad at all, from that viewpoint.
Doing this will make your characters more real, more relate-able. In fact, once all the viewpoints are given, the reader may even side with the bad guy, if the argument is strong enough!
So, have fun writing. Do not get bogged down in review at this stage. And make your characters real!