Neglected common knowledge

• Just because the support doesn't have a Sightstone doesn't mean they aren't warding.
• Sightstone or no, the ward limit is still three.
• Don't order the support to deep ward, and then yell at them if they get caught two seconds in.
• Full melee champions can't poke. Period.
• Death is the hardest crowd control, but it's also the hardest one to apply.
• Thresh gets stronger from souls. Let him get to the big crowd of minions first before you blow it up.
• You get gold from the Relic Shield, too.
• Mages should be taking care of the siege minions.
• Surrender at 20 or don't, but with five minutes to go, still, you might as well make an effort.
• You, too, can apply stacks to Braum's passive.
• You're killing enemy champions to open up objectives. They're a means to an end, not the end to itself.
• The AD guy should focus the turrets.
• There's no such thing as kill-stealing in a teamfight.
• An assist is still a modest sum of gold.
• A death given on both sides in a 1v5 just offered the equivalent of three kills to their team.
• If you were fed, four kills.
• Your champions' win rate is not YOUR win rate with that champion.
• Your 12/0 kill streak last game means nothing in this one.
• Rank is not an absolutely direct indication of skill.
• Never dive a Blitz or Thresh.
• Never dive a Morgana.
• Ideally, the ward mule and ward buster should not be the same person.
• The ward buster should have greater than average attack speed so they can smash and run.
• The support is usually just poking to farm spellthief's edge and maybe their mastery passive. It's not the signal to dive in.
• Trinkets can be upgraded for a pittance.
• With diligent and frequent warding, you can cap out on ward placement with the Greater Stealth Totem ALONE.
• Was it so wise to go 5 AD against Taric? Even with armor pen, you're going to have a rough time.
• The small nerfs to your favorite champion didn't ruin him.
• Leash the jungler. It's an investment to the security of your own lane. He's going to remember whether you did or not.
• Telepathy is still not a thing. Call your roles.
• Call your roles early. Ten seconds before the deadline is not acceptable.
• Twenty seconds is not acceptable.
• Thirty seconds is not acceptable.
• You aren't impressing anyone by autolocking.
• Three people just autolocked for the same lane? You have 80 seconds to compromise.
• You should have a sizable list of champions you're skilled with, just in case they ban or pick Yasuo.
• Last pick is just as coveted as first pick. You can see what everyone has selected, and no one is left to counter pick you.
• Holding the game hostage, aka "mid or feed", is juvenile and grounds for reporting. Don't do it, even in jest.
• If the same dragon has been warded three times, it's time to take it. Don't save it for later; that's when the enemy plans to take it.
• If the line of scrimmage is up against the enemy turret, get some hits in.
• If the line of scrimmage is up against your turret, all bets are off; the support is going to take a few minions.
• Thresh is retreating from the line, but a smart Thresh has his lantern ready to give you a head start back to your turret. Keep smashing theirs.
• Your chat ban after your last game isn't because of your behavior for THAT game; it's for a consistent pattern of misbehavior across several others.
• Unless they're Pantheon, Sion, Twisted Fate or they have teleport, a jungler on the other half of the map or dead won't be ganking you any time soon. Keep your wards ready for when you CAN'T see where they are.
• Just because Ezreal, Ashe and Jinx have a global ult doesn't mean they should constantly fire it to the opposite end of the map.
• Especially if it's parallel to the lanes.
• Especially if you keep missing.
• Stand behind Braum.
• Especially if there's an enemy Ezreal, Ashe or Jinx.
• Especially if you're low on health.
• Let him take a few minions to heal you.
• Don't pursue Singed.
• Especially if he has Liandri's Torment.
• If there's an enemy Teemo, stand two or three minions behind the one in front.
• For all we know, your "smurf" is actually your main account.
• It doesn't matter what name you just gave me. I have no way to verify that.
• Nor do I care to.

There will be more later, but this is all I can think of for now.