Most any website on the subject is going to try to sell you their "how to package". Much like the late night infomercials on network tv, they make pie in the sky promises but don't tell you the truth: You need to have solid industry experience and a generally strong understanding of business, which honestly can't be learned from a "how to". Your best bet is to work for an agency (in an office) for several years to get some solid experience and an understanding of how it all works. Then, you'll need to either locate some investors, save up a substantial pile of cash or secure a loan. You better have a very solid understanding of finance and accounting also. You will live and die by the numbers.