I share mine i learn the hard way : don’t auto walk and look elsewhere looking on wowhead or you end up in the sea in fatigue zone before you notice it 
Also don’t level up profession until a certain level, you will get faster gathering profession at max level than a low level that may die soon
As expressed long ago by a Guildie of mine: Don’t ride and read 
Also Guild chat can be dangerous.
My tips are old, some smart, some stupid, but I hope one or two is new and/or useful to somebody.
Your front is way tougher than your back, and you do more damage. So if you know (as per 2.) that coast behind you is clear, this can save you.There are many tips shared on the US forums.
Don’t forget layers, don’t accept group invite from a friend if you are in a dense mob area, accepting the invite will put you in your friend’s layer where the mobs have not been cleared and will surround you (this was shared by a blue post).
If you notice even the smallest connection problem, go to a safe place asap and stay there, 1 evening loss of progress is better than 1 month loss of progress. Do some crafting, sort your bags and bank or just log off.
Never overestimate rare and elite mobs, better return when you gain few levels than risk everything.
Never forget to use your CC abilities.
Don’t get bored of grinding weak mobs to gain level before trying more dangerous ones.
Don’t forget your available buffs. I almost died last night because my buffs had expired.
Life potions are a life saver.
Don’t do dungeons if even 1 member of the group cannot be trusted.
Do not immideatly delete or transfer your character upong dying to try again or you risk loosing your character name. There is addon called Death log that shows dying players globally and some may see your nickname and will try to reserve it for himself, hoping that you would delete or transfer character immideatly.
Watch out for areas with densly packed mobs. Server has this thing called hyperspawn and it activates when a lot of players are around. Some say it even works in cross layer affecting other layers too. Do not go deep leaving potential mob respawn behind your back. Think of several exit ways.
In case of doubd, kill only green lvl mobs and do quests only when they become green in questing journal
Level 3-4 defias in Northshire are easier than 5-7 kobolds in the cave.
When you’re level 5 after Northshire, stay at the farm until level 7, it’ll make the rest of Elwynn much easier, and takes mere 20 mins.
for the first week and maybe even longer in the starter areas: WATCH OUT FOR HYPERSPAWN POINTS. This can’t be stressed enough. The only 2 times I almost died at 10% hp and mana was only because 3-4 mobs spawned back to back, I mean the instant I kill one, another spawns on top of me and so on.
Always hold onto CC/Root for murlocs/gnolls/humanoids that will drop under 20% hp.
Be very very very careful going into caves. Only go in as far as you consider you can make a quick run for it if things go nasty. That means usually 40-50yd range into the cave. Always go in if there are at least 4-5 players inside as well, so if mobs do start spawning, you can share the burden between all and survive.
Make tons of consumables like myself, focusing on Alchemy, First aid and Cooking whilst being a paladin, should help me survive and never ever rush!
Depending on how far you get, create a bank alt and keep most of your gold stored there. Dying and losing 400g would feel bad.
Don’t group with hunters. Some hunters are damn good players, but most are absolute garbage and will ruin your dungeon run with their poor pet control. You can’t tell which hunters are going to be the small minority of good ones just from a “hunt, inv dps” message.
Currently the economy doesn’t exist, you can buy green pieces off of the auction house for almost vendor price. Spend some money, get some gear. If you’re a caster that can use wands, make use of all the people selling cheap wands.
Download the ‘hardcore unlocked’ addon. It wont help you at all, but the deathlog is funny to look at.
Caves are bad. If mobs that you need to kill spawn outside of the cave, then kills those instead of going deep inside a cave. If mobs respawn and you can’t run you are dead. If you do need to go in a cave make sure your HS is available to get out of dodge when things go south.
For Warlocks. The voidwalker is only okish until lvl 30 max. Don’t gamble your life on it’s poor tanking abilities.
Hesitate and die. (Many players try to run from a close fight, just to die from other mobs when running)
Better to act than react. (Plan your escape, plan your cooldowns for the boss).
Let the healer/caster Regen mana Mr. zug warrior (fast isn’t smooth, and mana users paying for massive amounts of drinks just so you can chain pull isn’t fair.
Eat between pulls for faster AND smoother runs.
If a player seems like they are new or just bad, dont help them, dont group with them and absolutely do not do dungeons with them. Dont feel bad for leaving mid dungeon if a player that seemed good suddenly starts to seem like a liability.
Some uncommon telltale signs of a liability player is:
Randomly standing afk for a few seconds here and there. That means they are looking elsewhere and not at the game.
Not responding in chat decently fast.
Asking about something that was just said in chat.
Asking any question in general that is common knowledge.
Tip especially for horde. Gravity kills.
Stand your ground. When you drop low on hp while fighting the mob, avoid exessive movement and panic running. You may end up pulling more mobs while fleeing and ultimately die when you could’ve survived.
And one more - remember train Unarmed weapon skill. One day someone unarm you …
Play it safe don’t get cocky like I did 
I’m avoiding murlocs like the plague
Never ever say “be right back”……oh wait; wrong thing.
On a serious note; avoid caves (solo) unless you outlvl the mobs by at least 2. 3 if they’re casters
Log out of your going afk
Don’t play when you’re very drunk………