I am by no means an expert on Dark Souls. In fact, I'm barely more than a noob myself. I've only played through the game once, and there is much I don't know, and much I probably could have done better.
What Is Dark Souls?
Dark Souls is an atmospheric, challenging action RPG title by Japanese developer From Software, originally released in 2011. Set in a gloomy, desolate fantasy world, you take on the role of an undead warrior, banished from the lands of the living, on a quest to learn ancient secrets of the world.
The game has a reputation for being rather hard. And I guess it is. You will likely die many, many times while playing it. But it can also be very entertaining and rewarding. And for all its hardness, the game is still, mostly, fair. You learn to deal with the challenges. You improve your character and equipment to help you overcome them. I'd say anyone with some experience with action games, and a little patience, should be able to beat it.
That being said, Dark Souls definitely isn't for everybody. If it's not your thing, that's perfectly fine. It's just a game, not some sort of holy grail, although some may portray it as such. From what I hear, the community for this game can be a little elitist sometimes. But you can just ignore such people. Remember there's no one correct way to play the game. As long as you're having fun, you're doing it right.
Do Your Research!
Here's the thing about Dark Souls: it tells you very little about anything. The manual that came with the version I bought is not very informative at all, and doesn't even list all the controls (for instance, I don't think it makes any mention of jumping—not something you need often, but occasionally useful). The game itself is not much better. While there is a tutorial section of sorts, it doesn't really hammer a lot of stuff in, or explain every aspect of the game. The menus may well be confusing. Like, what do all these stats mean?
However, there is a wealth of information about the game online. Several wikis are dedicated to it. (Here's the one I ended up using most.) You'll find more detailed info about locations, enemies, items, NPCs etc. For a game like this, I don't think there's any shame in doing your homework. There are so many things you simply cannot know. Once you get some way into the game, you'll likely want to explore more on your own, but getting to that point is much easier with at least a little more information than the game gives you. The story of the game isn't hugely complex, and the style of storytelling quite minimalist, so you're not likely getting a whole lot of big spoilers if you read up on some stuff (heck, it might even clarify some plot points that aren't necessarily all that obvious from the game's dialogue).
Early on, watching other people's experiences can be valuable. I watched Alex Steacy and Graham Stark of LoadingReadyRun play the first few hours of the game on the LRR stream, which I'm sure was helpful. (Here's the first broadcast of Graham playing the game, archived on YouTube—it's fun and also informative.) (There's also a post by Alex giving advice to new players here, which I recommend, though I'm covering some of the same ground in this post.)
The class you pick determines your beginning stat levels and starting equipment. But over the course of the game, you can increase whatever stats you want and use whatever gear you want; the class is only your starting point. So the class you choose isn't hugely important, although it does give you a small head start in certain areas and you may wish to focus on those areas. Some sources have recommended warrior or knight for beginners, as they're fairly straightforward melee oriented characters, and I have no argument with this. You might not want to trouble yourself too much with magic on the first playthrough. (I played a warrior and used almost no magic, and it worked fine for me.)
The gift is probably even less important than your class in the long run. Many of these are of very little consequence at all. Some are single use items that would be soon expended, so they don't seem especially valuable. The binoculars you can actually obtain fairly easily quite near the beginning of the game. Be wary of the description of the Tiny Being's Ring—it does not, in fact, regenerate your health, only gives you a slight increase in total hit points. The Old Witch's Ring allows you to speak with a particular NPC. It doesn't really affect the game, but is a fun little scene. (You can obtain it late in the game, but it requires a little work.)
The one gift that actually has a significant game impact is the master key. This allows you to open several doors in the game before you get the keys for them. I have seen some sources recommend it, but it's a double-edged sword. It might allow you to skip some potentially difficult areas early on. But it might also give you early access to areas that are too tough for you, and confuse you about where you're supposed to be heading. And if you're playing for the first time, do you really want to be skipping content anyway? I, at least, wanted to experience the whole game, from beginning to end. So I would only recommend the master key if you really know what you're doing. (Note that the thief class gets the master key as part of its starting gear, so beginners might want to be equally wary of picking that class.)
General Gameplay Considerations
I played on PS3 and have no experience with the PC version, but I have heard many people heavily recommend using a gamepad rather than mouse and keyboard. The game was obviously designed with consoles in mind.
Kicking is useful against enemies that constantly hold their shield up. It's a little tricky to perform, so you might want to practise it. Parrying is supposedly a really effective technique, but if you have trouble getting the timing right, don't stress over it too much. I beat the game just fine without learning to parry. Backstabbing is a little easier to do and quite effective against many slower enemies, so you might want to practise it.
Remember that you cannot pause! While you're in menus, you can still be attacked, so make sure you're in a safe place before you adjust your gear of whatever. Also, make sure you're fully out of the menu when you continue, as you can still move but you might, to your surprise, not be able to block or attack because there's still a menu tab selector active in the corner...
Once you do something, it's done. You can't go back. There's only one save file per character, and the game is frequently autosaving. When you quit, you carry on from where you left off. However, there's not a whole lot of things you can screw up permanently. If you use or dispose of an item, it's gone. Some you may be able to replace, others not, so take care. If you kill an NPC, they're gone for good, so be sure about what you're doing in such situations.
If you're ever stuck at a certain point, there may be other areas you can explore, and you can usually also grind and level up or upgrade your equipment.
While Dark Souls is primarily a single player game, it has some online features woven in. The most noticeable (apart from the many messages popping up all over the world) is the ability to 'invade' other players. You will get invaded, sooner or later. It is quite possible you'll die, since the invaders are likely more experienced players and likely to have better gear. Some may be actively trying to troll other players.
But, overall, it's not really that bad. At least it wasn't for me. You can only be invaded while in human form, and you can play much of the game just fine without restoring your humanity. (You will want to do it every now and then to kindle bonfires, though, and in order to summon NPCs to assist you in boss fights. But those are the only important times.) There's a cooldown before you can be invaded again, too. At worst, invading seemed like a minor annoyance. At best, it can even be exciting, especially when you actually manage to beat the other guy. Just be mentally prepared for the possibility.
There are several useful items you can get around Firelink Shrine when you first get there (in the nearby graveyard, and down the lift into New Londo Ruins). Getting some may practically involve suicide runs, but that's fine, because you keep all items when you die.
Try talking to NPCs more than once. Sometimes they have more useful information, gifts etc. if you talk to them two or more times.
Find the merchant in Undead Burg. He's got some useful stuff to sell, and there's a bonfire fairly near, so grinding for souls isn't too hard, if you don't have enough. The repairbox is really useful, especially if you use gear with low durability. You should probably also buy the residence key. When killed, he drops the uchigatana, which is a very good sword for anyone going for a dexterity-heavy character build (I pretty much used it as my primary weapon throughout the game). But if you do decide to kill him, make sure you buy everything you want from him first.
When you get to the bridge with the dragon, you can fairly easily get the Drake Sword by shooting its tail from a location under the bridge. You'll need a bow and plenty of arrows, which you can buy from the merchant. It might take a few tries to get the aiming right, and dozens of arrows before it drops the sword. Once you get a little further in the game and start upgrading your gear, the Drake Sword is easily outclassed, but at this point in the game it can be really good.
If you kill Lautrec when he shows up in Firelink Shrine, you'll get a rather good ring. You'll miss out on a storyline involving him if you do this before ringing the second bell, but it might still be worth it, and easier at this point... (Just make sure you never remove the ring, though, as you'll lose it!)
Before you head into Blighttown, go to the Darkroot Garden from Undead Parish and kill some of the tree creatures. They drop varieties of moss, which cure status ailments and can be quite helpful.
There's probably important stuff I've forgotten, and obviously I haven't gone into a lot of detail about the game's mechanics and controls. But you should be able to find a lot of this on your own, if you're interested.
I don't know if anyone who might find this useful will ever stumble upon my blog. But if even one person out there actually finds this helpful and ends up enjoying Dark Souls as much as I did, I'd be happy!