Having been networking for over ten years I know, for me, it is still the best form of promotion. I tend to find that advertising doesn't give me the same return and feel this has a lot to do with nature of Graphic Design. It is very hard for potential customers to quantify what it is that a Graphic Designer does and therefore they are far more comfortable using someone who comes recommended or they have met themselves.
When you start networking I would suggest that you try as many groups out as you can before you commit to any. Then choose the groups that feel right for you. The ones that you are comfortable with and that are convenient will be the ones that you make a regular effort to go to and that is very important. Below are a couple of networking groups you can look at to start with and maybe i'll see you there for a cuppa and a chat.
BA (Hons) Graphic Design