Seen a few newer players lately jumping straight into weird bluffs and fancy plays way too early, and honestly I reckon that does their head in more than it helps. If I was showing someone the game from scratch, I wouldn't even bother with the flashy stuff at first. I'd start with folding heaps more, paying attention to position, and just learning which hands are worth continuing with before the flop.
Position is the big one for me. New players underrate it badly. Acting later makes life so much easier, and acting early with rubbish gets expensive real quick. Same with calling too much because a hand looks "not bad"... that's where the leaks start. A lot of beginners would save themselves a stack of pain if they just played tighter and stopped trying to win every pot.
Other thing I'd drill into them early is betting for value instead of always trying to outsmart everyone. If you've got the best of it, bet. Sounds obvious, but plenty of people check because they're scared of "scaring them off" and leave money sitting there. Then they randomly decide to bluff in spots that make no sense. Bit backwards really.
Curious what the rest of you would put at the top of the list for someone brand new. Do you start with hand selection, position, pot odds, bankroll stuff, reading player types... or something else completely? Keen to hear what experienced players here think is the first lesson that actually sticks.