I wanted to provide a link over to Jay Bland's guide because I feel it's a fairly straightforward and readable guide to understanding ideas like meditation, centering, channeling, and out of body experiences (OBE's). For me personally the centering advice has been the most helpful; this guide is his rationale of the process, so it is from his own experience and point of reference.
This process is similar to learning to play an instrument or learning a new sport in that we develop our own technique over time, and it may take some practice. And similar to these other activities, everyone can do it but may be able to do some things more easily than others. Also these skills are not prerequisites to one another - someone may be able to naturally be able to get out of their bodies but not have the slightest inclination to meditate. Along the same lines, you can center without meditating, although some may find it harder to center with distractions around them.
Other areas of interest that are similar to these skills are spiritual healing methods such as Reiki, Martial Arts training, and making "higher self" connections. Reiki training can be helpful for understanding how energy works; level I deals with personal protection, basic healing methods, and understanding of chakras (your body's energy centers). Martial Arts training can be useful for meditation and centering, and building your awareness of your body in the space it occupies. Higher self connections can be defined as your creative energy, and may be experienced by toastmasters when they give speeches without notes, or writers who write an entire novel in the course of a single weekend. It's also known as "being in the zone", something I'm sure many of us have experienced at some point in our lives.
Something that could be seen as prerequisite for channeling is understanding personal energy protection. There are a number of different ways of doing this. One is to use energy to protect yourself; envision a beam of white light coming down from the sky, enveloping all parts of your body, and then down into the earth. Another way is to state that you wish to connect only with beings of the highest Christed Consciousness before you channel. Using a gatekeeper archetype or entity is another method: you will need to ask an entity you've previously connected with to be your "gatekeeper", and this gatekeeper will assist with connections to other unknown entities. "White Cloud" is apparently one such entity who can help with this.
In my process, I do some basic centering to clear my thoughts; in my case, I think of a white piece of paper. Then, I follow the advice of Peter Pan. I think of something I'm really grateful for or that makes me really happy (for example, my family, or ice cream!), and this provides a clear pathway with which to do other things. I then state my intent in my mind of what I want to do, for example, "I want to heal my back pains using Reiki" (this is the stage where you would want to do your energy protection if you are channeling). And then I would commence to do what I need to do. Note that you may not need to run through this whole process again to do different things unless you feel you need to. Once the energy is flowing it can be tasked for anything you want to accomplish. Statements of intent are not required but can help make the the thing you want to accomplish easier.