More and more folks are seeing raid signups on their calendars now, as even many casual guilds are starting to get the raiding itch. Chances are, you may be feeling like you want to get back into raiding and pronto. but that doesn't necessarily mean that you -- or your fellow guildies-- are actually ready to raid.
Once an expansion gets to be more mature, it gets a lot easier to set minimum requirements. With this one still shiny and new, and based upon my own experience with two level 85 shadowpriests and one level 85 boomkin, here's what I am seeing as being raid-ready.
Check Your Gear
Although the trade recruiters are specifying ilvl 345 minimum, that's not necessary, or in some cases attainable pre-raiding, for some casters. Wand-users have a tough time of it as compared to the relic equippers who can have a 346 item crafted. One of my shadow priests lucked out and got the wand from Grim Batol. The other is stuck with an ilvlv 318 green wand. That green brings down her ilvl (she's 340, wearing 2 epics) and keeps her from the Cataclysmically Superior achievement. It doesn't make me a bad player or her not raid ready. She's smoked people with higher ilvl gear in heroics. This is specifically why I would discourage raid leaders from having across the board hard-and-fast requirements at this point in the game. Better gear can help you eek out a little bit more damage, but it can't play for you.
Shooting for ilvl 339 and above is probably a better target goal for your shadow priest. This is reachable through running the max level dungeons, crafting some gear, buying some badge pieces, and having a few lucky heroic drops. Next, you'll want to make sure you gem your pieces with blue quality gems, enchant them, and reforge off any extra stats (such as mastery or extra spirit/hit.) If you are about to object and say "but why would I waste time enchanting gear I am just going to replace?" you might want to reconsider starting raiding at this point. Start of an expansion raiding is not a cakewalk. It needs everyone to give 110%. You will be wiping, and repairing, and rinsing and repeating. If you think you are being put out by spending $100g on a gem for your gear, you may want to wait til you can outgear the content.
Check Your Output
I have been grouped with folks in heroics through LFD who can only eek out about 4-5k. This doesn't cut it in most heroics, unless your other 2 DPS are rock stars, and your healer's mana pool can support a protracted boss kill. In a raid, no one can afford to carry you. If you are not able to hit 9-11k consistently in heroics, you are not ready to be thinking about raiding.
If you are close to the 9k, start looking at how you can fine tune. Try pulling back on some of that hit, shooting for closer to 10% hit than 14-17%. This means having to keep an eagle-eye watch on your debuffs to ensure you cast another Vampiric Touch if the first one doesn't land, but it can make a boost in your DPS in the long run. I swapped out my glyph of dispersion, which I loved for leveling, for the SW:D glyph. I also make sure I have my personal buff food on hand (Severed Sagefish Head) in case there isn't a feast or BBQ put out. I also come armed with a flask of the draconic mind or a stack of speed elixirs. Yes, these consumables cost a ton. But a raid is a team effort.
Try and Try Again, but Know When to Quit
So you are invited to your first raid -- awesome! Get in there and modify your rotation and work on adapting your playstyle for the on-the-move style of these new raids. It can take some time to get into the groove and to understand a new encounter. But you will also want to make sure you are able to ID when you are not up to the challenge.
For instance, if your team is repeatedly coming very close to killing the boss, but not quite making it, take a look at the damage meter. Are you hitting your target DPS? What about overall damage? In the event that you see there is a wide gulf between you and the DPS right above you -- or worse yet, there is a tank above you in the raid encounter -- you may need to give yourself a time out before your raid leader has to. It is important to understand the difference between needing some fine tuning or needing to focus a little harder, versus being in denial about not coming close to the requirements for an encounter, and having the expectation that someone else will pick up the slack.