How do I develop more passive income?

Developing passive income takes time and can be somewhat methodical unless you strike gold on your first try. Basically I would try to create a good stream of income from 1 project say a website and once I got that website to its goal of say $500 a month I would keep reinvesting some of the money into the website to keep it going strong and take the other money into my next project say a rental house or a small business that will yet earn me even more money. So now I stil have the $500 a month coming in which could possible grow over time and then your other project starts to earn its goal of $500 a month so now we have doubled our money and will keep doing this until we are at our overall goal which you should set from day 1 so you have something to work toward. This all sounds easy in theory, but it does take time to build these properties or websites up to there full potential.

I have read the key to wealth is turning earned income into passive income. What is the best way to do that?

Yes I believe one of the keys to wealth is having mulitiple streams of passive income or at least one strong stream of Passive income. I believe Real Estate in the form of rental properties is a strong form of Passive income, but if we are going to base into internet marketing terms then you could look at website building as the same thing. You can take a website(comparable to a property) and build it up and make it look good and flip it for quick cash or if you have build a nice stream of passive income with this website then you can keep just collecting money every month and hopefully use that money to make more and more money in other various income streams.

So basically take the money your earning with your main job or project and buy another house, website/blog, another job, an investment of any sort and make another stream of income out of it so then without any additional out of pocket money your income is gradually growing.