If you want to be financially independent, then you must create residual income. There are dozens of ways to build this type of income but what you should choose are ways that will last for a long time. Since it's hard to tell which streams of income will last longer than others, the safest way to do this is to build multiple streams of residual income. You can do this several ways.
The first thing you need to do is to pick one method that you are interested in building. It could be buying and owning real estate. It could be owning stocks and writing covered calls on them. It could be starting a business and building it up and finally hiring people to run it for you. It can also be starting an online business like a website. Whichever method you choose, start on it right away.
As you get more experience in the method that you chose, you will need to build more than one. For example, if you were to start a website, instead of just one, build multiple sites. Instead of just buying one home, buy multiple homes. Of course, some of these methods will take more money and time than others so you will need to take that into consideration as well.
Things can always go wrong. If you just have one source of income and for some reason it's taken away, you'll be left with nothing. Most people are living this way right now with their job being their only source of income. By building various ways to create income without you having to put in much work after you build it up, you will be truly free to retire and not have to worry about money. The important thing, again, is to start building right now.
Leon writes on a blog about how to build residual income where he teaches people ways to create ongoing income.