Here is another really easy way to start incorporating passive revenue into your existing business: match passive revenue streams to your services. What I mean by that is that you should be creating products and opportunities that align nicely with what you are already offering.
We create and design WordPress blog sites at BSETC and we often get asked, "Why do you design for WordPress instead of designing on HTML." So, we created a one-hour audio program, for free, that discusses why WordPress is the best website platform out there.
By creating a free product that touts the benefits of a service you provide, you are helping your potential customer to create trust in the software / technology / service / etc. that you are using or referring. It helps them to better understand the process and they will be more able to make an educated purchasing decision.
It's also a great idea to create passive revenue streams that can be packaged with existing products or services. For example: creating a Twitter 101 e-book that is sold whenever someone purchases a custom Twitter background but that can also be purchased on its own. The idea here is that a potential customer can get a Twitter background made anywhere but they may not be able to get the Twitter background made AND get a Twitter 101 e-book with it.
Services that get packaged with products have a higher value so think about that when setting up your services. You may be able to earn $97 for a coaching session, as an example, but pair it with an "After the Session Handbook" and you can easily charge $147.