What helps you maintain focus and interest in a long term project? Are there any tricks or best practices that help you there?
Recruit fellow sickos.
Really!
Nothing has helped me to write this book more than knowing there is a non-zero amount of people who are at least a fraction as interested in the characters and their story as I am. Even better if some of those people are your beta readers! (because it turns out those can turn into supporting writers really fast)
Though to be fair, it's not really sustainable to find your entire motivation in other people. imo you've got to be the biggest sicko of them all, the one who's the most invested in your brainworm OCs—because without you, no one else will ever hear their story. This is one of the most important things keeping me writing: I gotta get Lou's story (and the Prince's, and everyone else's) out of my head and into the world, so they can live on in more than just my brain
they deserve this, at the very least
(oh and write regularly!! hahaha that's a big part. make sure you keep writing, even if it's just in your notes. keep the story fresh in your mind so that when you take breaks and you go out walking or doing the dishes or what have you, the ideas bubble up and coalesce into even better plot threads you can weave into the next chapters)