The media genre generally is placed in the future and develops more on the fact that the future may not end, but may not be pretty either. Generally the storyline centres around some form of technology.
The more recent lifestyle that has evolved and coined this term is fragmented and hard to classify. It is still very new and there is debate on what the term means. Generally observation shows that "cyberpunks" are not only extremely technologically proficient, but are innately adept at it. They have a desire to know all forms of technology they come into contact with. Their attitude tends to be somewhat apathetic towards anything that doesn't directly involve them and their style of dress and personal tastes tend to be eccentrically futuristic.
In fiction, cyber punk is considered a sub-genre of sci-fi, especially popular in Japanese animation (anime), although also seen in films such as Blade Runner and The Matrix. Generally, this type of fiction covers the subjects of computing, hacking and general mechanical technology.
It should be noted that cyber punk is not an officially accepted term in computer science, although it has been widely accepted as a laymans term in fiction.
As far as a look, it's hard to put a figner on it. I dont think any one look can be described as cyber punk, its more of an attitude. Black jeans, tight t shirt with holograms, and leather jackets are a good start. Maybe toss in some Chuck Taylors, or combat boots. Some goggles or head phones might make good accesories.