Just start writing.
If you're asking questions like this then it means you haven't even started yet. You don't know what your process is because you haven't developed one yet. Getting into the habit of writing is more important than any specific way of going about it.
There's multiple ways to approach it. Some people do extensive prewriting so they have a structure to follow as they go along, some people just start writing and see what they come up with (aka discovery writing), many do a combination of both, etc. etc.
Putting in the hours is the most important thing.