I have six rental units which are a good source of passive income. I don’t use a property manager because you are right…they take about 10% of your rent. There are really only 2 things that tenants call about: 1. A plumbing issue 2. Heat/Air problems. Just find a plumber and heat/air guy you can trust. I travel a lot for my primary job. When a call comes in from a tenant, I can call the repair guy in just as easy as a property manager.

I like the way you have listed the ways to earn extra income and was quite surprise that you did not make mention of network marketing, which is a way to make extra income without quitting your regular, though most people view mlm as a pyramid scheme but the real pyramid scheme is a regular 9 to 5, because you can only have one president of a company at any given time and network marketing business model to promote product that can be used is really cheap to join and can offer a substantial extra income or what do you think?

I am still working on my passive income, however I like multiple income streams even more. My favorite is capital gains because it is one of the lowest rates. One of the best passive income streams is a pension/Social Security. As I near retirement, I like the concept of it supporting my needs and my 401k supporting my wants. In addition, my brokerage accounts are all at capital gains rates. Don’t misunderstand, I am still working on adding more because I like multiple income streams!
Real Estate Crowdsourcing – After selling my SF rental house in mid-2017 for 30X annual gross rent, I  reinvested $550,000 of the proceeds ($810,000 total) in real estate crowdfunding, based in San Francisco. My goal is to take advantage of cheaper heartland real estate with much higher net rental yields (8% – 12% vs. 2% – 3.5% in SF) and diversify away from expensive coastal city real estate which is now under pressure due to new tax policy which limits SALT deduction to $10,000 and new mortgage interest deduction on mortgages of $750,000 from $1,000,000 for 2018 and beyond.
This campaign is a great viral marketing example of where the benefits must outweigh the cost as those against Nike’s messaging started to post videos of them destroying their branded apparel and refusing to support the company again. If you are planning on taking a side within your viral marketing campaign make sure you measure the benefits and costs as it could involve you losing customers and ultimate money in the long run.
Marketers and agencies commonly consider celebrities as a good influencer with endorsement work. This conception is similar to celebrity marketing. Based on a survey, 69% of company marketing department and 74% of agencies are currently working with celebrities in the UK. The celebrity types come along with their working environment. Traditional celebrities are considered as singles, dancers, actors or models. These types of public characters are continuing to be the most commonly used by company marketers. The survey found that 4 in 10 company having worked with these traditional celebrities in the prior year. However, people these years are spending more time on social media rather than traditional media such as TV. The researchers also claim that customers are not firmly believed celebrities are effectively influential.[43][44]
Definition: Unique Selling Proposition or USP is the one feature or the perceived benefit of a good which makes it unique from the rest of the competing brands in the market. It is that very reason which motivates a buyer to purchase that product even though it might be costlier than other products. Description: Unique Selling Proposition or USP is a very important concept used during the time when a company promotes its product through its advertisements in both TV as well as print media which eventually attracts a consumer to buy a particular product. The key to boost the sales of the product effectively through advertising is to highlight the USP of the product prominently. Unless you highlight the USP, consumers will not be tempted to buy your product. Every product should have its own USP, which makes it stand apart from other products in the similar category. USP is different for different products. Let’s take an example of a restaurant which is very famous across the world for its quick Subway Sandwiches. The company makes the sandwiches healthier for consumers. Consumers who are looking for a quick meal can walk into any subway outlet and get a quick sandwich made, which contains nutritional value. In this way the company is able to create its own niche market across town in India. The USP of the product is a nutritious sandwich at an affordable price. USP is a very important component in developing the product. A strong unique selling proposition makes you stand apart and also plays an important role in branding your product. But, USP alone can guarantee to a product’s success. Superior product quality and at par service, both before and after-sale are very important in creating the foundations of a market for a product. Always remember, with a distinct USP, the company doesn’t even have to bother about competition because if you have developed something which has not been developed by others, then you are the only player or a market leader in that specific product category (Example – iPpod by Apple).
^ Semenov, Alexander; Alexander Nikolaev; Alexander Veremyev; Vladimir Boginski; Eduardo Pasiliao (2016). Analysis of Viral Advertisement Re-Posting Activity in Social Media. Computational Social Networks. CSoNet 2016. Lecture Notes in Computer Science, Vol 9795. Lecture Notes in Computer Science. 9795. pp. 123–134. doi:10.1007/978-3-319-42345-6_11. ISBN 978-3-319-42344-9.
Viral marketing is any marketing technique that induces websites or users to pass on a marketing message to other sites or users, creating a potentially exponential growth in the message's visibility and effect. A popular example of successful viral marketing is Hotmail, a company now owned by Microsoft, that promoted its services and its own advertisers' messages in every user's email notes.

Let’s say that you sell motorcycle parts. You may find that your customers like videos showing motorcycles in action on Instagram and Facebook, part review videos on YouTube, articles about the latest technology on Twitter, and GIFs made from your Instagram and Facebook videos for Imgur and Reddit.  In short, you’ll need to make some videos to get your products embedded into viral content.

For starters, many websites are using them–so there’s a big market for stock photography. It’s no shocker either, as one study found, that 65% of people are visual learners. In fact, when people hear information, they remember about 10% of that information three days later, but if a relevant image is paired with that same information, Brain Rules found that people retained 65% of the information three days later–a 55% increase.
It’s easy to think as passive income as money earned while sitting on a beach sipping mojitos, but there is lots of work involved, says financial coach and retired hedge fund manager Todd Tresidder. If you’re worried about being able to save enough of your earnings to meet your retirement goals, building wealth through passive income is a strategy that might appeal to you.
There is debate on the origination and the popularization of the specific term viral marketing, though some of the earliest uses of the current term are attributed to the Harvard Business School graduate Tim Draper and faculty member Jeffrey Rayport. The term was later popularized by Rayport in the 1996 Fast Company article "The Virus of Marketing",[12] and Tim Draper and Steve Jurvetson of the venture capital firm Draper Fisher Jurvetson in 1997 to describe Hotmail's practice of appending advertising to outgoing mail from their users.[13] An earlier attestation of the term is found in PC User magazine in 1989, but with a somewhat differing meaning.[14][15]