I actually spent a year and a half working as an affiliate marketer (mostly selling drumming related products – lessons, kits ect). 5 years on and one of my one page sites (which I’ve not touched) still nets me about $150 a month. I won’t be retiring off that but only really now appreciate the reverse pyramid approach to entrepreneurship (working for nothing initially but later being paid without effort!)
What I Do: I’ve set up multiple investment accounts outside my main operations bank that deals with working capital e.g checking, paying bills. By transferring my money to a couple brokerage accounts and two other banks as soon as it hits my main bank I no longer have temptation to spend on frivolous things. As a result, I can wake up 10 years later and reap the rewards of compounding. My 401(k) is the best example where constant contributions over 18 years has grown to over $500,000 without any savings pain given it just became a part of life. Real estate is also a fantastic asset class for the long term. It’s fantastic to enjoy your home, pay down your mortgage each month, and end up with a paid off asset that has likely appreciated during your time of ownership. 
These days, low-risk bond yields aren’t enough to meet most income needs. When investing in bonds, the income typically comes as coupon payments – contractually guaranteed interest payments at predictable intervals.  There are many kinds of bond income available, so you must strike a balance between reaching for higher income (yield) and limiting risk.
In January 2018, I missed my chance of raising the rent on my new incoming tenants because it didn't come to mind until very late in the interview process. I didn't write about my previous tenant's sudden decision to move out in December 2017 after 1.5 years, because they provided a relatively seamless transition by introducing their longtime friends to replace them. I didn't miss a month of rent and didn't have to do any marketing, so I felt I'd just keep the rent the same.
Multiple Streams of Income is chock full of advice. The investing advice is also great and certaintly better than what you will find say in JBQ's ridiculous book which cost many people millions in lost dollars. I saw a review here by Mr. Donoghue. My guess is that some people will try to bury that untill mindless 1 star reviews. If you can scroll back and read it, I highly recommend that you do. It shows a system of investing that yielded huge returns even during the Clinton "bear market."
"For long-term savings, investing in low-cost index funds is the ultimate passive strategy," Goudreau says. "As legendary investor Warren Buffett recently told CNBC’s On the Money, 'Consistently buy an S&P 500 low-cost index fund. I think it's the thing that makes the most sense practically of all time.' By not picking individual stocks and, instead, buying a low-cost fund that tracks the market, you pay less in fees and take less of a risk. Then you can sit back and watch your money grow over time."

An obvious example is over exposure to bank stocks, which have been excellent investments for over a century.  Though a foundation of most portfolios, bank stocks do involve more risk at certain stages of the economic cycle than many realise.  Being less exposed to bank shares in the last few months could have preserved some capital.  So, a more diversified approach can help mitigate some of these risks.