What to write first
Question: I have followed your 10 step guide on how to start writing a novel, and now have a fully planned novel. Now where do I start writing? Should I start with the first chapter and go from there, or write the most important chapters first?
Most people find that it works best to start at the beginning of the story and work towards the end in chronological sequence. This mirrors how the reader will eventually experience the story and the way events and information build upon each other.
For instance, if you write a later chapter first, you may feel the need to put in information (to make the sense of the events and characters) that might actually be better established in an earlier chapter. Later, when you write the earlier chapter, you may find yourself duplicating information.
Writing in chronological order (but with an outline) makes it easier to see how tension is building. whether the story flows well, and how well you are preparing the reader for what is coming.
That said, there are other approaches you can choose other than writing in chronological order.
For instance, often a story begins after the inciting incident. The reader learns about the inciting incident later on, through flashback or some other device.
If the manuscript will present the events of the story in a non-chronological order, you may find it helpful to write it all chronologically first, and then move parts around later.
Sometimes writers will write the climax or the end of the story first, because they want a clear idea what they are working towards, or simply because that's what calls to them.
You are, of course, free to find your own preferred way of working, and you may have a different approach for every book. The important thing is to follow whatever route feels clearest and easiest, and evokes the most passion. Writing a novel is a long haul, and there is no need to make the process harder.