Dark Souls

- You lose souls (currency and xp combined) and humanity on death, but you can retrive them by absorbing the green orb left at your corpse. If you die on your way there though, they're gone. So. Early on, don't hold on to thousands of souls, especially if you're going into uncharted territory. Spend them on items and levels, you don't lose those.

- In the same way, you can consume the soul items to gain souls the currency, only use them right before you level or buy something.

- You can wear heavier armors but the big thing is blocking and dodging, especially dodging. How fast you can roll and otherwise get the hell out of the way of an attack that is almost certainly going to wreck most of your health is dependent on your Equip weight. Dark Souls appears to have several more levels of equip weight than Demon Souls, and I think the fastest one we know of is at 10% of your equip weight.

- For the love of god, get the Orange Soapstone (or whatever it's called) from the first merchant, because without it you can't write messages or rate them. And writing messages (whether to be helpful or troll newbies) is one of the best parts of the online. Also, rating messages positively will make them stay around longer, which is good for the ones that are actually helpful.

- You must have a specific item to cast spells. Pyromancy, Miracles, and Sorceries each require a different item (Pyromancy Flame, Talisman, Catalyst respectively). You can refill your casts of a spell by resting at a bonfire.

- By offering Humanity to kindle a bonfire (must not be Hollowed to do so), you can increase how many Estus Flask charges it will give you to rest there. By default, it gives 5, but you can upgrade it to 10, 15, and I believe it maxes out at 20, but I'm not that far into the game myself, so someone can correct me on those if necessary.