Register for a fundamentals course. You can find these courses by browsing classes listed at colleges near you. While you can learn much of blacksmithing from home, you should still learn the basics from someone more experienced. This is especially important for the safety aspects of blacksmithing.
Find an area of your house that can be converted into your forge. Generally this will be the garage area. You can also set up a shed in your backyard to be your forge. There should be no flammable objects near your forge, including grass.
Start building up your arsenal. Don't overload yourself with tools in the beginning. Start with just your anvil, hammer and tongs, then work your way up to using more advanced equipment. This will also help keep your initial investment low.
Take on different kinds of projects and learn how to make different objects. The skills you'd need to make a decorative bed frame are completely than the skills you'd need to make a giant wok.
Join the Artist-Blacksmith Association of North America (ABANA) to meet other blacksmiths, learn new techniques and compare notes.