The first really critical step is to figure out your expectations. This means figuring out what kind of raider you plan to be and what kind of raid group you want to join. If you want to upgrade in a short time, you can Buy WOW Gold to help you achieve your aim. Theses are important things to consider, so take your time with them.
Lastly, if you are the ultra competitive player and have a whole ton of time to spend raiding then you may have what it takes to be a hardcore raider. Think carefully about this though, if you do get into a group you will be expected to be there each and every time a raid is going on or risk being kicked. ADPS greatly outnumbers all other class types and so there is a lot more competition for a DPS slot in a raid.
Therefore DPS players will generally take longer to find a raiding guild and more is expected of them right off the bat. These are the basic types of raiding guilds. There are others that skirt the lines between the categories, but in general try to determine who you are and where you would fit best.
Remember, even if you want to be a hardcore raider, if you can't dedicate the time don't waste your time or theirs, do what you are able to do. This is important when you first start out as you are going to be turned down a lot, especially if you are trying to get into a hardcore raiding guild. Looking for a casual or middle tier raiding guild will not be quite as bad, but still takes some time.
Therefore, when guilds go to recruit they tend to be very picky. They know they will be spending a lot of time with a player and are looking for someone that either fits with them socially or play style wise or is the absolute best regardless of personality. Even though you want it, your personality may not mesh with theirs and you may have to keep looking.
Expect this and be ready for it, after all if a guild is too easy to get into, would you really want to be there to raid. We all start someplace, so even if you are fresh to max level and not in a full epic setup, make the effort, show that you care. In order to bring convenience for you, we store a lot of Cheap WOW Gold. Sure you may still have some blue items, sure you may need some upgrades, but do the best with what you can before you apply. Don't expect them to take you in crap gear. Look for best in slot blue items, epic crafted items, badge items and anything else you can.
Then gem it, enchant it, and basically make it the best you can. Even thought you will replace items, it shows you are trying to make an effort and know your character. Raiders can look at a character and see if you truly understand the class. Are you a rogue and gemming for strength, hmm may not get accepted. Now that you have done all your research and gotten ready, most of your work is actually done.
You know what you want, where you should fit in, and are ready to go. Take some time and put in some effort on the application. Most raiding guilds have websites and online application forms. Even if you talk to them in game, most will refer you to the website to apply. Take this seriously, it is your way to tell them about yourself. Sell yourself. This means you need to give them as much information as possible. If the form is 10 questions and you answer in 10 sentences you are probably not going to get in.
On the flip side, don't give them your whole life story hoping that they will let you in just because your dog died last week. Keep the information relevant and enlightening about your self. State who you are, what you bring to the table, what you are looking for, and why they should pick you. Show that you care enough to spell check and grammar check. Explain yourself completely and in an organized way. Think of this as applying for WOW Gold a job and you won't be far off.