I've said this elsewhere, but the key thing when thinking about "Magic the Gathering's storyline" is that it's a lot like "Marvel comics' storyline" or "DC comics' storyline": Lots of individual narratives kind of woven into overarching ones, with occasional plot points relating to things that happened years ago IRL in stories that half the time aren't quality enough to justify tracking them down.
The good news in general is that they're getting better at this, with more recent Uncharted Realms stories basically summarizing The Story So Far for any given plot thread (and I second the recommendations for Uncharted Realms and the other mothership resources). The good news for Ravnica specifically is that both blocks actually had legit novels for their main storylines (though I haven't read any of them myself, so I couldn't really endorse them per se):
Original Ravnica: Ravnica, Guildpact, Dissention
Return to Ravnica: Return to Ravnica, Gatecrash, Dragon's Maze
EDIT: Formatting
Ravnica: City of Guilds or The Brothers' War
Depending on the place, you may see the second getting credit, but I think despite that, there's few people that actually know about it.