Don't worry too much about being derivative. Slice your project up: finish one section, do the next. Don't edit while you're writing, and don't worry about format right away - you can always go back and reformat things, and having a strict format right away means if something cool does occur to you, you are less flexible. Don't shoot for full color 400 page tome level of writing. If you lose inspiration, take a break and write something else for a bit. Ask for help on things you don't know that well, whether it's setting detail inspiration or just layout. And have at least some income already, if possible.