Channeled writing is quite a popular mean of expression amongst mediums and psychic workers. It is possibly the simplest way to channel, even for those that have difficulty with other means. But, although I think (in my opinion) that it is probably the easiest method it encounters the same difficulties as all others. Because in order for it to work you really need to let go of your thinking brain, your left side brain.
Writers will know the feeling I describe. Or musicians or any artist that all of a sudden has an “inspiration” and starts “free-flowing”. Automatic writing works in exactly the same way regardless of where the information comes from (subconscious, spirit guides, lost souls, higher beings etc).
I usually have drifting thoughts and I recognize them as different so then I relax, grab pen and paper and start to write (or paint but usually I get colour images then). If you are not an artist nor used to work with your intuitive right brain you can still try. Exercise it by drawing (does not matter if you are good!), practising writing with your left hand (or right if left-handed), singing, meditating and anything that does not involve logic thought or focusing on a task. Free flow, let it come through no matter how silly it might seem or how it does not make sense. In fact the first few times it probably won’t and even after you become more accustomed to it is still not an exact science. Do not expect to write sentences in perfect grammar, that is not the point. The calligraphy might be (often is) totally different from yours and words my be foreign. Automatic writing is not about you sitting at the word processor and writing a piece (that would be creative writing), it is about channeling information and words from sources beyond this plane therefore it is expected that they won’t sound like you have just dictated them!
Find what you feel comfortable with (meditation, music as an example) and try it out, dedicate a journal to it and try as often as you can. Like with dreams make a point of trying to interpret the writings and the symbols that might be contained within.
An example of channeled writing (by me) can be found in my post Channeled messages