I've been working on article for the magazine on this topic, but with the Raid coming next beta weekend I thought I'd start this as a conversation here on the forums first. Feel free to discuss!
Raids in GW2
We learned recently that Heart of Thorns will include new 10-man PVE Raids as it's "challenging end game content". We've seen a trailer and some articles  , and we know that there's a weekly lockout and some nifty rewards like Legendary Armor. But we won't know exactly what raiding in Guild Wars 2 entails until we get to try it out. In the meantime we can talk a little about raiding in general, and how we might prepare for raiding in Heart of Thorns.
Is Raiding for you? The Five C's
I started raiding in MMOs back in 2000, in Everquest, and have done PVE raiding in quite a few MMOs since. There has been a lot of variety in just about every aspect of Raids across these games, but also a few constants. I call these constant factors the Five C's.
Raiding isn't for everyone. Some folks find it too frustrating, some find it too regimented, some find it too time consuming. Give the Five C's a read, and consider whether raiding is a fit for your personality, play style and schedule.
Raids are Content
MMOs have lots of things to do in them, and raids are another thing to do. You bought the game, so you should be able to play raids too, right? I agree! But that's not to say raids are easy content, nor are they solo content. Becoming skillful and knowledgeable enough to do your part in a raid team will probably take some work.
As with any challenging content, there is often a bit of drama about elitism among raiders. There are plenty of extremists at both ends of the argument (too hardcore! too casual!), but there is also a giant kernel of truth at the middle ground. If you are 'that guy' who doesn't bring your gear, skill, knowledge, communication, cooperation and commitment up to snuff, you are probably holding back the other folks in the raid. This is particularly true in 10-man raids!
Bottom line: want to experience raids? Awesome, I hope you come out! But you'll need to put in the work--it's only considerate of your fellow raiders.
(Good) Communication is king
You'll need to be on voice chat, at least to listen. Raid encounters are fast paced and it's simply too slow to coordinate actions in /party or /squad.
In addition, you'll need to be disciplined in your communications--particularly during combat. Keep your status updates as short as possible. And don't talk over the commander!
There is usually some time for questions and socializing between attempts, but even here be considerate of your teammate's time. This is probably not the best time for an in-depth trait by trait discussion of your build, for example.
Finally (and importantly!) try to keep your cool in voice chat. Raids provide ample opportunities for frustration, no need to crank it up even further with emotional outbursts in voice chat. I find the best policy is to take your finger off the push-to-talk button and swear fluently in the privacy of your own home. :)
Time for a little Commiseration
Expect to wipe during raids. Over and over and over. Mistakes are how we learn, and you'll be with nine other friends who also have to learn from their mistakes. It takes time for it all to come together.
Over the years I've found that this is the aspect of raiding that is most likely to turn some folks off. They feel frustrated by the wipes, or impatient with others are who not doing their part successfully yet. Something to consider if you are someone who becomes frustrated or impatient easily.
Doing your part: Cooperation
You can't win a raid encounter by standing in a corner and auto-attacking. You can't solo that raid boss either. Your team needs to work together in many ways large and small to pull off a win.
Sometimes you'll be tasked with a role (blasting fields, breaking breakbars, etc.) that you don't routinely do. Sometimes you'll be asked to change your class, or build, or utilities. Winning requires flexibility and teamwork from every single person on the team.
Doing your part: Commitment
Waaaay back in Everquest, I did some raids that lasted all weekend long (with breaks only for meals and sleep). That kind of mega-hours commitment is no longer the norm for MMOs, but some commitment is still needed. The reason is simple: nine other people are dedicating a few precious hours to the raid, and your own commitment is a way to be considerate of their time and preparation.
Given the flexibility of GW2's combat system I don't expect raid groups to require fixed rosters or regular attendance. If you want to raid, however, you should commit to learning the encounter and getting your skills and gear up to snuff. Also, commit to the entire time scheduled for raiding on a given night. If you know you will to have to step away for 30 minutes in the middle of the raid, for example, please be upfront with your team before the raid starts.
If you are OK with the Five C's, raiding can be very fun! I love the feeling of beating a tough fight with my friends. Good times, great memories!
Next up: Things You Can Do to Prepare