OK, wall of text time. :D
Pull up a chair, young'uns.
I usually warn my players that I have one main rule.
Stupidity kills. If you go to dead:DEAD, then you are gone. Roll up a new one.
There are no potions of resurrection.
Cloning is still in its infancy. Decades of religious objections and the crash didn't help things. Naturally, the corps aren't always toeing the line, but on the whole, as far as the public is concerned, clones are still SF.
Yes, combat IS lethal. Not quite as lethal as 2013, though.
When EVERY solo was packing a FN-FAL because one shot was enough to turn most people to dogfood at close range. Full auto was just 'fine red mist' time.
I don't go out of my way just to kill them, though. Maim them, hospitalise them (and watch that eat away their creds. Medical care IS expensive. This will probably mean they end up owing someone.) It's all about leverage.
I didn't do the "dim the lights, put on a blacklight and have them all wear shades thing. It's a cliche and you can't see shit.
As for advice ... READ "Listen up, you primitive screwheads". Really read it. Absorb it. There's a lot of useful advice there.
I've had the privilege of GMing MaxMike through a game of 2020, and he was the consummate gamer throughout. He also gave us lots of useful advice. Let me tell you, whilst he's a lot of fun to GM, it's also a lot like inviting Robin Williams and Billy Connolly onto an interview show and expecting to retain control - all you can do is hang on for the ride! He never took direct control, but he wasn't a PASSIVE player.
Don't be afraid to borrow stuff from movies and books you've read. Watch some movies (Watch the remake of Total Recall - JUST for the scenery and work out how to describe life in the colony as opposed to life in the Shiny world.
Decide on a power level. Don't be afraid to set limits. I personally don't let PCs start with a special skill over 6. Yes, they are supposed to be the badasses, but there should always be someone MORE badass than them.
I had what you could call "power gamers" in my campaign. They milked things to get shiny toys. I had them stolen. They did it again, I had a hacker they'd annoyed in the past (they did make enough enemies) zero their accounts.
Above all, you are telling a STORY. The players are the main characters, playing their parts - you just have to maintain the rest of the world. If they get out of line, punish them, but warn them first. Escalate the punishments.
They cross a local mob lord, for example.
Send a couple of bruisers around to rough them up. NOT the combat characters - the non-combatants - the netrunners, the fixers, the techies, etc. If they fail to back off, have one of their apartments blow up, kidnap family, send them body parts, etc.
Give them each time to tell their parts. To grow their characters. It's about them making the best of a bad situation. They are meant to be the heroes in a world without them.
I hope some of that helped. I have no current rpg group - the locals are only interested in D&D or Pathfinder, so I confine my SF gaming to Infinity.
Hey! Where'd ... Everybody ... go?