Any experience artisan can manage to draw anything for you. A specialist in portraying may need just few hours to create a beautiful person for you.
Now, what is the difference here? Probably the sheer number of portraits he or she has done before.
How many novels have you written so far?
See, no wonder you don't know where to start. A picture takes hours or days, so he or she could have created thousands of paintings. Most novelists are not that accomplished by wide margin.
The best approach I would recommend is to split your work into three main phases which comprise:
- writing, and
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And no, I have no notes whatsoever. I've just been telling the outline for myself, designing so the frame I have to put my next writing into. But of course, you are free to make notes, mind maps, or raw sketches as much as you need and want.
You can even write independent chapters. Today, with text editors nobody cares in what order is book written as soon as writers rearrange their novel in the polishing phase.
However, I would suggest writing in small pieces, called scenes rather than chapters. One scene up to 600 - 2000 words, depends on how diligent you are.
Trust me, to motivate yourself to write a scene in two days is far easier than to have done one novel in a year.
The last polishing phase comes after you have something to work on.