There are 10 classes in World of Warcraft and each of them is very different, bringing in a number of different strategies and tools to make gameplay more interesting. However, if you're just getting used to a new class or are just not having a good time with an old stalwart, you need to determine what you're doing wrong and how to develop better strategies for your situation.
• Does Your Talent Spec Do the Job – Always start by analysing your spec. Your talents might be completely out of whack or maybe just a talent or two away from being perfect. Whatever the case, make sure to rethink how you spec your talents and choose a way to build your character that matches what you're doing with it. See wikis and your fellow player for tips on which talent specs will work best for you.
• What Kind of Rotation Are you Using – Next up, make sure you have a good shot rotation. Each character class is designed to have an ideal makeup that will allow them to deal higher damage, or heal for more or stay alive longer. Learn what it is and then learn how to adjust that rotation under duress. You want to maximize output, while keeping from running out of mana or whatever you need to perform those attacks.
• Gear and Item Check – Finally, you need to check out your gear and items. There are so many options in there to choose from, but if you have blue gear going into a raid, no wonder you're having trouble. Check what you can afford and what is available and then max out your stats as much as possible. These are the things you need to be doing to be topped out for your class.
Every class in the game is designed to let players excel in exciting, different ways. If you don't actually spend the time necessary to learn your class though and tweak them to the degree that is necessary for optimal play, you'll never be able to get to those upper echelons of excellence. So, what options do you have? To start with, you can practice. Second, find other class members to help you out. Finally, get some good strategies off of forums and wikis to help you choose talents and get the right gear. Only with the right information will you ever truly succeed.