Okay, here is the idea: What did you learn from (preferably old) games?
Post a few things that come to mind.
I'll start:
1.Giants: Citizen Kabuto: If you are fighting a blood thirsty giant, aim for the groins.
2.Nethack: Hmm, I don't want to lose these wands of cancellation. Perhaps I should put them in my Bag of Holding filled with artifacts? Also, water walking and Planes of Water don't really mix...
3.Redneck Rampage: The holes in outhouses can lead to the strangest places...

Morrowind: Mixing mushrooms and random leaves will make you stronger and smarter.

Duke Nukem 3D: 101 ways to psyche yourself into thinking you're awesome.
Doom: It is possible to run with increasing acceleration, making Usain Bolt look slow in comparison
Thief: That as long as you're standing on a shadow, you're invisible.
You can completely piss a person off, and then gain his respect by giving him $1000. Also, if you give a person $10, he may not forgive you, but still take your $10 anyway. This is a cheating, dishonest world.

Diablo 2: You can experiment to find new recipes yourself... Or, if you don't have 10 million billion items to try out new combinations in a hit'n'miss fashion, you can go on the internet and find the recipes there.
That game always needed an in-game recipe system.

Morrowind: Don't trust an Imperial, they all are assholes.
Half-Life series: Gravity is a bitch.
Doom 3: Nothing is scary if you know the mechanics of a horror film.
Every zombie game EVER made: Aim for the leg or head.
I wish to stop.

Max Payne: If you are a hard-boiled (read: emo) ex-detective, no matter how many sexy women are surrounding you, you'll never get any.
Max Payne Again: Enemies with superior numbers and firepower can be overcome by running and diving in slow motion.
Max Payne Yet Again: Negotiation never works. The only way to ensure your own survival is to shoot the crap out of anything that seems the slightest bit threatening. If you don't kill something now, it'll probably come back to kill you later.
Still Max Payne: Don't be fooled; those hobos might not be able to afford houses, but they can still afford guns. The hookers are armed too, but it's anyone's guess where exactly they were keeping the firearms...
Max Payne 2: It's fairly common for people to survive bullet wounds to the head. To treat a bullet-wound to the head, just administer CPR.
More Max Payne: Painkillers are yummy.

Hmm so many things
Ultima: It takes a remarkable individual to be truly good
Grim Fandango: That love requires sacrifice and that all things end
Planescape Torment: What can change the nature of a man, how nothing is quite what it seems, how pain attracts pain, how words are more powerful than weapons, how... well I could go on forever with this game
Neverwinter Nights 2: Mask Of The Betrayer: Sometimes you just can't win no matter how strong you are
TIE Fighter: That I hate little more than treason and that I'm a better pilot than than Vader
Dawn Of War 2: If I throw a frag grenade at an enemy, it automatically becomes the enemy that FenixP decides to charge (Honestly he's like a dog with a ball)

And how do you know this? Maybe he is suicidal.

Well I've seen it happen a dozen times, I toss a grenade and he sprints after it likeI've asked him to fetch it. If he was suicidal he could stand there doing nothing whilst tyranids slice him to bits

Tyranids...I only played th tabletop game for a month and enjoyed it. Maybe it's puppy love with grenades?

Pong: Blip.
Tetris: A lesson in construction.
Dead Rising: Anything is a weapon!

Except objects that wont glow when targeted...stupid trees.

Bah Humbug!

I heard that they had thought about having recipe scrolls as extra drops, but this hasn't made it into the game... they've changed it for D3 so I imagine it won't be so bad. Thank god for the interwebs...

Mass Effect, Tales of Monkey Island and others: What you're trying to say is seldom what actually comes out of your moth.