Pick your PuG
Actually, that's simply the worst extreme of PuG raiding. The reality is usually more pleasant, although rarely as smooth as guild runs, as long as you keep a few things in mind.
Call me elitist or fussy, but I quite like to know a bit about the randoms I'm going to spend the next few hours with before I tag along. For something like a Karazhan pug, you should be able to see the group members via the LFG system -- the Armory is your friend. Check the tanks and healers especially, but if there's a DPS member that's seriously lacking (in gear, clue or both) be prepared for frustration if you decide to join.
If you're in reasonable gear (a lot of PuGs require full epics, for example -- which you can't get because no raid or heroic groups will invite you!) then you should be able to pick your group, especially if you're a tank or healer. If you've done the best you can but you've still got a large number of blues, your chances of getting a group won't be as good, but if you have friends who are going they may be able to get you a spot if they can vouch for your skill. Be aware of your key stats and what numbers you should be aiming for -- a tank turning up with 10k health won't go down too well, even if all his gear's purple.
A few key things to look out for when inspecting a potential raid member: is the gear (particularly epic pieces) gemmed and enchanted? How do the base stats look? Where's it from -- PvP, crafted, or tier gear? Do they have a PvE spec? What are the weak points in their gear and how easy would they be to replace? What drops will they likely be after? Are they in a reputable guild? Make your Own
Maybe none of the groups going suit you, you're secretly a megalomaniac, or you've simply been burnt one time too many. Creating your own raid is harder work but ultimately gives you control over the run, and whenever I hear people complaining they can't get into Kara groups because they're "just another rogue", this is usually my answer.
If you know the instance well, have a good idea of which roles you need to fill and which classes work well together, and don't plan on acting like a spoilt child by kicking someone if they outroll you, then why not lead the raid yourself?
This gives you a chance to vet everyone's gear, deal with frustrating group members directly and generally make sure everything goes smoothly. However, finding the raid members might be hard. If you've got a couple of bored guildies, a friend in another guild, and access to LFG you should be ok -- if you don't really know anyone, you might end up "LF1M Tank" for a few hours as your group slowly falls apart. Don't give up hope; making a note of likely prospects and good players for future reference can help speed this up a bit. Semi-PuGs
Especially with 25-man instances, a true pug is rarer (at least on my server) than a partial guild run. These "semi-pugs" usually start off with some guildies, then friends, then friends of friends... The fact that a guild is at the core makes some things smoother, as people generally have well geared mains they can bring if stuff starts to go tits up, tactics are at least generally agreed upon, and there might even be voice communication of some sort. However, these can run into problems if you end up with a lot of members from multiple guilds trying to do things their own way, rather than compromising.
The advantage to getting in with a guild is that the same group of people might be doing regular instance runs and, by proving yourself, you can get invited back. Depending on your situation you might even end up raiding with them -- that's how I got started with raiding, over two years ago. Alternatively, you might run across a loose alliance of people
who regularly PuG the same instances -- organised via forum topics or similar. PuG Etiquette
We all have our own definitions of etiquette from 5-mans, especially heroics, but things get more complicated when you add in more players. As with alt runs, it really helps to be clear on loot. Most people I've seen tend to run with a "need if you need" system for 10-mans and rolling (sometimes with master looter) for 25s, but make sure everyone knows beforehand, and if anything's unclear (especially if it's a guild run and there's a chance of some rarer items dropping) check beforehand.
Much as I would love to convince every player to have some sense of fairness when it comes to random rolls on loot, the best I can really say is to have some knowledge of the loot that drops for you and for others. Don't get blinded by purple fever and roll on anything with a vaguely useful stat -- maybe that spirit offhand isn't all that great for a shaman!
As with 5-mans, behaviour like inappropriate pulling, consistent overaggroing, extended AFKs or disconnects, rolling need on every item etc. can and probably will be dealt with; of course, there's the opportunity to have a bit of fun in raids, but don't make life a pain for other people or you might find yourself removed from the raid. People in random groups tend to be a lot harsher than on guild runs -- in my experience, they expect the worst.
Strategies and Suggestions
Generally, the strategies used in one Karazhan run won't differ much from another, but there are a few places where you might want a bit of clarification before beginning -- an example would be which kill order to use on Moroes, or what you're going to do with hatchers and birds on Jan'alai. If you're running with two full tanks things will be different from a setup with a main tank and occasional offtank; maybe you're used to having a lot of AoE but this run is melee-heavy. Don't expect every run to be cookie-cutter and stay flexible.
If you've got suggestions about the raid, be they positive or negative, you can choose to air your thoughts openly or in private. Making sensible comments openly can boost your credibility (this guy's clearly been here before) but if you keep it up constantly you'll look like a know-it-all; bashing someone in whisper might make them nervous and more prone to mistakes, but making open suggestions about how DPS could have improved in general might make the next boss easier. It's a matter of finding the right balance between helping the leader and becoming a hindrance. And if you are the leader?
Learn to take criticism; although it shouldn't be a major issue in PuGs, tensions can run quite high if you do wipe to the tougher encounters. Set the raid up for success, ensuring groups are organised for synergy, you've got a main tank list and some idea of a kill order (whether that be a main assist or tanks marking things with skull), everyone's got Omen and you're broadcasting boss warnings.
If you're the tank as well as leader, it becomes a lot easier to make sure things work the way you want, as you can control the speed of pulls and generally take charge of the entire run. If you're not a tank, however, and your tank is sub-par the run can seem to go on forever. Motivational techniques such as yelling "pull" in raid warning have been known to work with surprising success in this sort of situation, although they do give one a somewhat fidgety reputation.
When PuGs go Bad
Sometimes the hero doesn't always marry the princess. Sometimes PuGs don't end happily. Whether through repeated wiping, drama or simply bad performance you might find yourself with half a raid (or worse, just a raid ID) and bosses left to kill. Don't despair! You can either choose to go through all the pain again and reform -- usually only worth doing if the loot you came for is on one of the unkilled bosses -- or simply accept that it wasn't meant to be and try again next week.
Runs that are missing a few members "from Curator" tend not to have the greatest of success in my experience (would you join a run that was clearly so bad they couldn't kill Curator, hoping the bad players were the ones who left?) but I've been surprised by them in the past, and you have nothing to lose but those hours of your life you spent spamming up LFG.
Another option is just to call in the troops. If you're PuGging a 25-man raid which is incapable of killing the end boss, be it Kael, Vashj or Archimonde, slowly replace the weak points in the raid with guildies until you achieve world domination or a boss kill, whichever happens soonest. Your guildies likely only need the end boss anyway -- but be careful of being accused of ID stealing or, worse, exploiting PuGgers if you regularly put together runs doomed to failure so you can sweep in and get an easy kill. Conclusion
If PuGging a raid is your only hope, don't despair. It can be a smooth process with a bit of background research and effort, but bear in mind that the horror stories are all true and grouping with people you know nothing about can go wrong sometimes
By contributing what you can or even leading the raid yourself, you can help avoid disaster, but don't expect to sit back and have an easy ride unless you get really lucky with your group members. Remember, challenges can be fun!