Stop Handing Out Experience
It’s been several years since I handed out experience and it’s very liberating. This cuts down on bookkeeping at the table and eliminates arguments about how much experience a specific event is worth. Your players need to know that you’re keeping track of it (I use a spreadsheet) and you should be ready to tell them how much farther they have until the next level, but that’s about it.
Turn On Inherent Bonuses
Having your players obsess about magic items because they’re lagging behind in a slot is hugely disruptive. They’re not thinking about story, they’re thinking about mechanics. Turning on inherent bonuses gets them thinking about other things.
Let Them Take It Back (Within Reason) and Set Them Up To Succeed
This isn’t chess, where you’re obligated to move a piece once you’ve touched it. If you force them to sweat the small stuff, they will slow down to avoid mistakes. They will also feel more frustrated when they forget something. Beat them down with strong encounter design rather than pouncing on errors.
Also, don’t be afraid to remind them when their character is about to do something stupid. Combat can get complicated and sometimes they either don’t hear you or they don’t think it through. Gotchas very rarely make something fun.