People often start to play trollish when they think game is won anyway because it's 18:7 or something like that.
They start to make risky solo plays 1 vs 2 or 1 vs 3 or in case of Yasuo even 1 vs 5 because they think they are immortal heroes now just because they are fed.
Just stop that and end the game clean and safe together.
If you have people like that in your game make clean announcements in chat what to focus next.
Another mistake is to try to end the game too fast or not fast enough.
-- Too fast:
Let's say you have enemy mid inhibitor but on sidelanes you have only one tower each. And enemy team is to respawn in 10 seconds.
Many people try to kill Nexus towers now. They overstay and die.
Better back up and push sidelines instead it's a save win.
If you have no minionwaves but 2-3 enemy's are dead for 20+ seconds (including Jungler) do Baron.
Or you can fake Baron to force a teamfight if only one enemy is dead.
In general the "lawnmower" tactic is the best.
Do T2 towers only after all T1 Towers are down.
If your botlane kill enemy bot turret they swap top, after that mid. If you have all T1 Tower you do all T2 Towers and so on.
If you just push one lane (i.e. mid) it's very risky to get flanked.
If your bot is fed and killed their first tower tell them to swap to top.
-- Too slow
The other extreme is when people don't realize they can end.
Don't do Baron or Drake/Elder when you could kill 2 Inhibs or even Nexus.
Group and end that shit instead of farming your jungle.
Port back (to shop) as team and not one after another so you have to wait everytime because always someone is base.
If you are winning don't waste time and dawdle around. You have to be effective. Every minute you waste is a minute for enemy's to catch up. Remember: your XP lead is worth nothing when they reach lvl 18 too.