The way I do it is that when I get the idea for a book or story, I make two different word documents: one is just the outline of the story and the other is the actual writing, so I can have them side by side on screen. It helps keep details and things in order as well as being quick to make sure everything you say is right and you're not changing anything you said previously.
As for writer's block, the way I avoid it is that I woke on multiple stories at a time, so that if I hit a block on one, I jump into the other, the different head-space of the different story-lines stops me from thinking about things other than what is blocking me so I can just return to the original after some time. Reading others also helps, seeing how other people worked through similar problems.
Check out my stories if you want, I write a lot of fantasy. Same name on Tapas. Sky-Garden, Shrouds and Stilettos, Rain and Deathblooded.