A lot of pretty classic but good advise, There is already a discussion on PvP, but here are two cool ones

Don’t overprepare. I have an inexpensive egg timer. My partner hates its ticking sound. So I use a watch instead. 30 minutes for a session. That’s how much I give myself.

That one is the biggest killer, beginner GM carefully think about tonight tavern, the innkeeper has a name and a description, the bard is going to tell a story about missing kids, there is even a menu for the night. Except that the PC are like There something weird in that town, May-be their food in poisonous we shouldn’t stay too long in the tavern, you’re right let’s camp in the wood and keep watch Tons of stuff prepared by the GM end-up in the garbage (Or for another session). So keep an outline, and as the author said, everything is a bonus.

Keep the game running and review rules after.

Looks like one of the most basic advice. May-be you forgot about how black-smithing works (To take the kind of rules you won’t use any time). But at the end, just find an appropriate skill/mechanics and problem is solved. May-be you missed a point and were too nice/harsh, but at least you didn’t spend 15 minutes re-reading a rules.

Be consistent and predictable.

This is IMO the best way to fix 90% of game planning problem, session occurs at a fixed date, not matter who’s there. Worst case, you do a board game, or have a drink. but if you wait for everyone to be available, you won’t play much

Clear boundaries. I have only two hard rules that would make me act immediately: no player-versus-player behaviour and no sexual violence. I repeat these two rules to each new player. I state them in a direct, no chance to misunderstand, manner.

I had something similar. It went like: No r?pe, no necrophilia, no needless child murdering, or other overly edgy shit. There is no debating this. I will immediately call you out and start a fight over that.

Never forbid Player vs Player, tho. As long as both sides were ok with that they could bash each others heads in. They constantly beat each other or kindled their clothes on. But miraculously never killed each other.

The “keep the prep time short” rule is interesting. Since my in person dm is mostly interested in building sets - that’s a huge reason he enjoys running games - we so try to keep on course when we know he’s like deliberately made an enormous swamp or something.