I have been playing Nethack 10+ years, and in that time have won twice (Once with a Tourist). Which if you know anything about Nethack, this is pretty good. The following are some words of advice I can give you about playing, they are not exactly spoilers, but I think they might help you.
The game should be called Netcrack, because it is the most addictive thing I've ever taken. I have been playing over 10 years, and have won twice, and I still keep playing the game. And I'm not alone; it is not an uncommon story for a student to get so enthralled with this game that they do it instead of homework, etc.. For this reason I feel that conquering your addiction of Nethack is just as important as winning the game. If you are getting too addicted to Nethack, Save your game, and come back later! Or if you are too compelled to keep playing, kill your character in a stupid way (This will probably happen anyway), and you will get so pissed off at being killed, you might stay away from the game for a few weeks. (Enough time to study for finals.) And if you think winning the game once will get rid of your addiction, it probably won't.
You can play Nethack for years, and never win. Reading the spoilers is nearly a requirement to have a chance in hell of winning the game. And even if you do read them, you might not win. In fact a friend of mine has been playing Nethack nearly as long as me, and has read all the spoilers but still hasn't won. [Spoilers Here] You should also get familiar with newsgroups, and read rec.games.roguelike.nethack.
Nethack is more about dyeing than it is about living. If you play, expect to die most of the time. It is best to have a reincarnation attitude, and to transcend the frustration of dyeing. You can always come back and start over, and if you want to win, you will need to do this a lot.
While it is tempting to cheat. I will tell you from experience it really isn't worth it. Nethack makes it fairly hard to cheat in a lot of ways. If you want to get the hang for the game, change yourself to explorer mode. This way you won't have to die, but you can't win either. Although sometimes even in explorer mode, you will find a situation where it is isn't worth living, as you will have too many bad guys to slug through, and you will keep dyeing.
Most death's in Nethack are what one would consider "stupid", and many are avoidable. When you get yourself in a situation where you are likely to die, step back for a moment. It is really easy to get your brain on auto pilot mode, to not realize you are in trouble, and die stupidly. So when things look bad, take a break, save the game, and come back. And when you do come back, don't rush, you have all the time in the world to think, since Nethack is not a real time game. Look through your inventory, and all of pouches. With a few right moves you might be able to save yourself. Pray only if you are really low on hit points, and don't forget about writing Elbereth.
Also, to avoid "unavoidable" deaths, get resistant to as much as you can, as quick as you can. Especially poison. Don't face poisonous creatures if possible until you have poison resistance, they will kill you more often than anything else. Get reflection as soon as possible also, this will protect you from most wands, and from death beams.
Praying to your god, can save your butt many times. But I recommend doing it only when really needed, as you may find yourself in danger again soon, and if you prayed frivolously you probably will just get your god angry, and die.
While there are many more powerful artifacts that exist in the game, when you are about to face the Wizard, have Magicbane in hand. In fact, before going down the Ghennon, I recommend using Magicbane as your primary weapon. (Gained through a wish, or sacrificing) This is because Magicbane will protect you from getting your items cursed. Which is one of the worst things that can happen to you, and can totally kill your game. It may take longer to kill things with Magicbane, but the protection is well worth while.
There are a lot of spoilers, but some will make your game much better, and make your character much more powerful. When you read through the spoilers, pay most attention to: Making holy water, Donating money to priests, Polypiling, Getting Magicbane, Getting the Orb of Fate, Getting the Platinum Yendorian Express Card, Making your armor / weapons rust / burn resistant, Gaining more hit points through potions of healing, and using Magic Markers to write Scrolls of Charging, Genocide, Identify, and Enchant Armor.
If you ever accidentally put a bag of holding or a wand of cancellation into a bag of holding, you will loose everything in that bag of holding. This really really really sucks. And is easy to do if you are not thinking. So my recommendation is to not worry about the wand's of cancellation, and there is never a reason to have 2 bags of holding, as one will carry everything you need.
Identifying wands is fairly easy to do, and worth while. Identifying rings is harder, but more important, as some rings will cause you a lot of problems. Potions and Scrolls are fairly safe, although if you are paranoid, you might want to take off any armor you don't want to loose before reading an unknown scroll (if you haven't figured out which one "Destroy Armor" is yet).
Some people say that the Barbarian is the easiest character to ascend with. But I think the Valkery is cooler, and gets more cool artifacts than the Barbarian does, so I recommend playing her. Just make sure you get Poison Resistance as soon as you can. The barbarian will often last longer because he starts out with this.
There are tons of jokes inside of Nethack. And I can't say that I know all of them, but the following books will help you understand some of them: The Hitchhiker's Guide to the Galaxy, Through the Looking Glass, Tolkein's Middle Earth Series and What is Quantum Mechanics?.
Also, Nethack is very much based off the D&D role playing game system. If you are not familiar with role playing, you might want to check out the new 3rd Edition of Dungeons & Dragons. Role playing in my opinion is a "more worthwhile" obsession because at least you are being social.