I often tell people that meditation is both the easiest and most difficult spiritual practice to master. It is easy in that any one can learn the techniques to meditate. There are also many tools available that will guide your through a meditation session.
Although I enjoy listening to guided meditation CDs at times, I spend the majority of time meditating in silence or with soft music playing in the background. Because I am a Christian, I use meditation as a way to spend quiet time with God as well as for the mental health benefits. Psalms 46:10 says "be still and know that I am God." I believe that it is during these quiet times with God that my spirit is transformed as well as renewed. Other additional benefits for meditation include stress relief, maintaining peace of mind, and controlling negative thinking.
Unlike a guided meditation, during silent meditation you don't have any prompts telling you how to relax your body or a descriptive narrative telling you what to do. It's pretty much up to you to guide yourself, but that is the easy part.
As I said earlier, meditation is easy because anyone can practice it. However, meditation is very difficult because most of us have a hard time quieting our thoughts and keeping our mind from wandering off. Because of this, some people give up prematurely believing that they can't meditate or it is to hard. But let me give you an analogy of what meditation is like, even what you might consider a "bad" meditation.
Have you ever burnt food in a pot? I have on many occasions. This is one of the worst things about cooking. Well, if you are like me you probably fill the pot with water in an effort to soften the burnt food. Later you come back to the pot with a scrub brush in hand and begin to scrub and scrub until you can start to see the bottom of the pan again. It may take you 20, 40, or 60 scrubs with the brush before you get all that debris off. However, with each scrub you are taking off a little bit more until finally, you have a clean pot again.
That is what meditation is like. Each time your mind wanders off and you bring it back to the present by focusing on your breathing, a sacred word or phrase, it is like one scrub of that brush and little by little you learn to quiet your mind and free it from negative and destructive thinking patterns. With continual practice you can learn to control your mind instead of allowing it to control you.
Therefore, you can't meditate incorrectly unless you give up and don't do it at all.