more often than not it intimidates me, too! and when that happens i just take a looong break, until motivation comes back and i get my ideas flowing.
i m sorry i dont really know what advice i could give you other than listening to songs, making mood boards, writing random scenes youve imagined would happen even if theyre waaayy later on in the story... you just have to get into the vibes of your fic, live in it basically.. motivation comes and goes, and it's okay to step back sometimes.