Wow thank you for all those helpful tips! I have this giant fic in my head about Ruby and Whale during the missing year but I can’t even finish writing the first chapter. I have all the scenes in my head but I just can’t put them into words… Maybe it’s because this is the first time I’m trying to write something serious. I think I’ll try what PriceofMagic said and write only what they say first and then add all the rest of the things.
When I have that problem of having a Big Fan Fic, I normally just start writing stuff and see where the journey takes me.