I would start at the local library and study all the various means of advertising. There are the obvious commercials, but many people tend to forget about more subtle and subconscious means of advertising (such as bumper stickers, road signs, sports venues, schools, sponsorship...etc.). Once you are familiar with the advertising methods out there, study web sites and web affiliate programs to become familiar with the advertising methods they use...look everywhere to get the overall picture.
Start a blog and use the various methods of advertising to promote it and pay extra for the traffic compilation. That will break every click, hit or route a visitor took to get them to the site. Once you learn all the effective methods of bringing in new visitors--then you will need to learn about the search engines...keywords, web crawlers, etc. Use the blog to check the growth of the popularity and search placement. Once you have the basic ideas for optimizing your popularity, you will need to build your portfolio.
Your portfolio will consist of examples of your work, show why the client should hire you and should showcase the work you do for other clients. I would suggest that you may want to consider doing a few free or low cost projects to help build your portfolio and client recommendations.
There is much more involved--but this may give you an idea of where to start. Hope this helps!!