My advice would be to focus on HOW to be successful at affiliate marketing first, the "good money" will come later.
Search through the affiliate directories, affiliate networks, CPA networks, affiliate OPM (outsourced program management firms) and find a few offers that interest you, that you think you might have fun promoting, and that you already have a bit of knowledge about. This will make the whole learning process a bit more interesting and less tedious.
Build your website, and try out a variety of promotional techniques to get traffic (PPC (small scale to start), Natural Search SEO, Article Marketing, List building, etc.) Play with your website design to see what provides the best conversions. Once you feel you're reaching some level of success, then start branching out into other niches and directions.
Just one affiliate program is not enough to guaranty a consistent income. What happens if that program goes out of business? The best way to go is to establish a multiple stream of income from different affiliates programs so when one went under, the rest continue to pay and every day life will not be disrupted. Building a passive income from several programs must be the foremost priority for everyone who wants to earn money for living from the Internet. This passive income is also called residual income.
Be patient, just like with any other industry, it generally takes some time and practice to get proficient.
Experiment a little and you'll discover your own "Best affiliate program".