A novel is made up of small moving parts. When the novel is published, the parts may appear to be in just the right place, to have always been where they are. This is rarely the case. Most writers move things around as they go, and move things around some more as they revise.
Don’t be afraid to write a paragraph here, a page there. Not everything has to be a full-fledged chapter in the early stages. If you have a scene in your head that you know you want to write, go for it. But if you sit down at your computer and feel flustered and uncertain, allow yourself the freedom to think in small bits.
Tell yourself, “Today I’m going to write 500 words about…” and go from there. There will be days, a few glorious days, when you wake up and know just what scene you want to tackle, just what kind of trouble you want to get your character into.
But there will be other days when the blank page seems blanker, and the hour or two or three that you have set aside to write seems destined to be wasted time. The next few pages are for those days. On days when you are stuck, when you just can’t seem to figure out what to write about, begin with 500 words.