When I decided to get into raiding I looked up the Armory page of the best mage I knew, a Horde mage who had been obliterating me for years in Alterac Valley. His gear gave me an idea of what I was lacking, and the item database on the Armory site will also tell you where to get most items. Then create a shopping list. Write it down somewhere, trust me, it will save you all sorts of time sifting through PUGs as you try to improve your gear. As you venture into raiding, you can expand your shopping list to include gear from the bosses you are running. This is also an excellent resource to keep you focused on the essential items. This way you can avoid the problem I got into where for a while I was picking up items that were not as good as what I had.
Spec: This is a big one. I know for my main character, I have had just about every spec possible, but when I made the leap into raiding, I decided to research raiding specs. WoW Wiki has a lovely guide on the various specs out there. Take a look and take your time. If you can help it, you want to minimize your respeccing costs, so pick a spec that will last you. Also, realize that some guilds will ask you to respec for their needs, but if you don't have the gear for a certain build (i.e. you're a resto druid and they want you to tank, but all your gear is + healing) then the respec won't do you much good. Let the guild know when you can, and when you cannot be flexible with your build. Honesty is very important here. You will be expected to be in top form for the spec you choose.
Attunements and Keys: Now that you know you have the best gear you can and your spec is chosen with care, it's time to build up your access to end game content. The first and most important attunement is Karazhan, and this will require you to run four instances, one of which is in Tempest Keep. This means that in order to get your Karazhan key you will need to have a flying mount. But its 1000 gold you say. Yes, and this is one of those items you are expected to get if you want to raid. Without a flying mount you won't get into Tempest Keep, which means no runs in The Eye for you.
Once you start working toward your Karazhan key, the next step is to start collecting the heroic keys. As I mentioned earlier, each guild will require you to have some if not all heroic keys before you apply. I say get them all. This way you can start collecting gear from heroic instances, and that will also help your chances with acceptance into a raiding guild. Remember, the better equipped you are, the most useful you will be. The more useful you are, the more likely you are to be accepted.
Mods: Like them or not, mods are a part of raiding. There is plenty of debate of which mods are best for their purpose, but in general most guilds will ask you to get the same ones: CT_RaidAssist or oRA2, CT_RABossMods or DeadlyBossMods, KLHThreatMeter or Omen, and usually Decursive. In addition they will most likely use some sort of VoIP program (at least until Patch 2.2), either Ventrilo or TeamSpeak. Download both so that you are able to be as flexible as possible. Once you have your mods downloaded and installed, make sure you take the time to get familiar with them. The middle pulling Attumen is not the place to be learning how to configure your Main Tank windows.
Guild: Finding the right guild is tricky business, and it requires a bit of research on your part. Knowing what kind of guild you are looking for and when you want to raid (you did do your introspection, didn't you?) you can then look for groups that will be a good fit for who you are. The realm guild recruitment channel is a good place to look, and if that is a bit empty on your server (I know it is on mine) then check out the recruitment forum. Better yet, the realm general forum will give you a great idea of which guilds have the type of reputation and personality that you are looking for.
Any raiding guild will have a website of their own, and by reading through their guild charter and their public forum, you can get a sense of who they are and if they are right for you. On the other hand, if the website is not maintained, or full of posts that seem somewhat fishy to you, take is a bad sign and move on. Picking a guild is much like picking a family, something we don't get to do in real life, so pick carefully. This is not the time to apply, you are just looking around to see what the guild is all about.
If you get the chance, group with a member of the guild on a run. Ask them questions. A strong guild will have members that can answer some of your raiding questions or direct you to someone who can. If the instance run goes well, if they know their business and you are satisfied this is the guild for you, then we move on to step three.
Next time Learn2raid will look at Application, with tips and tricks on how to apply successfully to a raiding guild. After that we will look at the terminology you will need to know in order to raid, and what your first raid will look like. Until then, enjoy that rep grinding.