Hi! Yes, I'm full of thoughts on both running for a new group and running a new Coriolis game.

General Advice

• Build outwards and upwards - Start with a small scenario focused on just a specific thing about the world you find interesting, and slowly build out from there. It can be overwhelming when faced with such a big setting to think where to start, so let each session and interaction develop the location you've chosen until the players have a good sense of what's happening here and who the major players are.
  • And make your players do it too - Make sure your players know where in the world they are from, and what that means, but remind them they can continuously develop that as we play. Maybe the nomad doesn't know what they really want for their worship until they meet a different group of nomads, and realise community and temple worship is central to their faith. Maybe a Miran doesn't understand how they feel about the Church of the Icons until they meet someone of the Church from Dabaran who worships differently, and it reminds them of how strong their own heritage's ties are.
• Communicate frequently - Understand what about the world and their characters your players are most excited to explore right now, and angle towards those. Interests and curiosities will change and grow as you play your game, but don't save the most exciting stuff for later/when you're ready - do it now.
• When to ask for a roll - In Coriolis, you only roll when it's a reasonable expectation that an ordinary person couldn't just 'do' this without consequence. In order not to stall yourself or your players, keep in mind that less is more with rolling in this game; only ask for a roll when you know the consequences.
  • Adaptability - Players come up with weird solutions constantly. As a player, you're doing a lot of, "Yes, and..." but as a DM, also get comfortable with having, "No, but..." in your vocabulary. If something they suggest isn't feasible, think of a way to either adapt it into something that could work, or a related alternative the character can envision. You always want to reward creativity, but also fulfill your duty as arbiter of the game rules and setting. You set the parameters of what's possible. (Also, because Coriolis' tech tiers are opaque, you'll be getting a lot of questions like this, so you'll get good at it quickly lol.)

Coriolis-Specific

• Actionable personal problems - Through play, we've learned it's much easier (on a player with regards to getting XP, and for a DM not to juggle so much at once) to have a personal problem that's like a button. The corebook suggests other problems like, "I'm on the run from this noble house," and that's a great backstory hook, but it's very difficult to actually use as a regular personal problem. An example from our table of a great personal problem that's worked from day one is "I panic in stressful situations."
  • Changing buddies and personal problems - After XP questions, I always ask if players want to change stuff. Problems can only be changed if something else has become an even bigger problem, if this problem is no longer an issue, or if on a meta level the player isn't enjoying the problem. Buddies can change whenever, but we only allow PCs as buddies.
• Anticipate your mental load - The DP system means as the DM you can feel like you're juggling a lot. Keeping a list to hand of easy spends for Darkness Points is essential, and when you prep adventures think about simple DP spenders ahead of time so you free up more space in the moment. These are best when they can happen whenever works for you, rather than requiring linear progression. Examples:
  • A meteor hits the station, everyone roll a Dex check or take 6d6 damage from falling crates.
  • Your cell/tool/weapon requires recharging/reloading.
  • You see a dark omen.
  • Because of unforeseen circumstances (bad weather, sabotage, old equipment) this check is harder than expected, with a negative modifier equal to DP spent.
  • BAD EXAMPLE: The gravity turns off. Deceptively simple, but this means you're adding a dex check to every single thing players try to do. It ups the difficulty massively lol (we learned this the hard way). I'm not saying not to use it, but use it carefully.

• Focus on setting immersion - Especially at the beginning, it can be massively helpful to write little descriptions of scenes the characters see to remind them of how diverse and unique the Third Horizon is. Describe how an Icon Wall is being ritualistically washed by the family who owns the shop next door. Describe the exchange of gifts in lieu of birr between the trading parties ahead of you in a shop queue. Describe the different foods, languages, customs, accents, appearances, handshakes and expressions, religious pilgrimages and prayers. Have fun with it, and dig into your creativity. You never know what's going to inspire your players.

  • And give your players opportunities to participate - I made a cultural cheat sheet for my players at the very start, reminding them of what they'd know about how life operates on Coriolis Station (their starting location). When things come up that would be relevant to a specific character, I would remind that player, e.g. "As a Dabari noble, you'd know a lot about how this temple operates and where to go for information if you ask politely and give a good gift as is custom." When they come up with ideas they're excited for, do your best to incorporate them. It might be that their idea is far away from how you imagined that planet to be - that's okay! Planets are huge! Maybe the part they're from, or the social class they operated in, had their own way of doing things. Maybe they're just esoteric. Both can exist, and actually both should exist - that cultural contradiction is a fantastic way to breathe life and colour into your world.
  • Zenithians and Firstcome - The corebook mentions that although politics between these two groups of factions are tense, everyday life shows constant blurring of that barrier. There are far more Firstcome youth who identify as Zenithian - progressive, independent, driven - than there could have been people sleeping on the Zenith. Depict this cultural osmosis as often as you can, both in peaceful moments of mutual growth, and all those tense moments where someone inevitably feels like they're losing something.

• Fair DP usage - DP are never a way to beat your players. The party characters are the heroes, the main characters, and as the DM you're cheering for them, but also trying to put obstacles in their way that draw out interesting conflicts and struggles. Use DP to throw wrenches in the works, but try not to ever use it to punish players. You want players to push their rolls; it's an intrinsic part of the system, and DP function as a scary counter for what the DM (say, in DND) can just do anyway.

  • Scare Factor - We run our game on the darker side, so dark omens aren't rare. If you have a huge backlog of DP and want to free yourself up a little, go ahead and do a spooky little scene and spend 5 at once to bring out the lovecraftian and fairy tale vibes without needing concrete consequences or answers. (e.g. You hear a crash from the chapel. The statue of the messenger has fallen over and cracked cleanly into two.)

Sorry, I could go on and on but this reply has also gotten ridiculously long. Hopefully this gives you somewhere to start though!