If you have a bow never shoot it straight up, the arrow will come back down and can hit you which may kill you.
Never blow up your armor stands. When an armor stand gets blown up it doesn’t drop anything so you will lose your armor. So make sure creepers don’t get near them.
Never attack zombie pigmen. If you attack a zombie pigmen in the nether than every zombie pigman in the nether will be after your head and wont stop for a while.
Never attack a wolf or ocelot. Wolves and ocelots are both like pigmen. If you attack one all of them that are near will attack you.
Never dig straight up or down. If you dig straight up or down there is a high possibility that you will hit lava and burn to death. thus making you lose everything you have on you.
Never eat spider eyes. Unless you are completely out of food then you probably wouldn’t naturally eat them. But when you eat a spider eye it gives you poison. So unless you have lots of milk then you would have been better off without eating them.
Never run around in the wild with items your not willing to lose.
Never try breaking into the void. It takes a lot of work and time and once you get in all thats going to happen is you die a quick and meaningless death losing all your items along with you.
Never look endermen in the eye. Unless your trying to attract an enderman to you to fight then don’t look them in the eye.
Never try to jump a lava pit, we would hope you wouldn’t try this because the heat of the lava will get to you and you will slip and fall into it giving you a slow painful death.