Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.
I found this to be a fascinating and most helpful book. It was so motivating I'm already working on three new streams of income, and about to start a fourth. Forget net worth! Cash flow is much more important, particularly if you're retired. Only one slight criticism of the book. It's a bit dated, but those few parts make little difference to its overall value. If you're currently struggling with how you're going to survive after you retire, try Allen's approach. It will open your eyes.
The obvious way to earn a second income is to get a part-time job. If you are not currently working, this is an excellent way to start as it gives you the freedom and flexibility to start other passive income opportunities.  The other option is to simply work from home full time which frees up commute time so you can focus on building more income streams.

Use your base to build your audience, and when you’re starting out, take advantage of the fact that you don’t have a big following to give more personalized help to your first fans. “The people who are starting out — that’s their advantage,” says Flynn. “They have the opportunity to speak directly with those people few coming their way to find out what their problems are and give them the special treatment that bigger brands might not be able to do.”
Came to the U.S. as an immigrant in 1968 from a poor Asian country with only $100 in my pocket. Took advantange of 401-K savings plan by contributing 10% of my pay. My employer matched the first 6% savings (50 cents/dollar saved). Did not know anything about investment so 100% of 401-k money was invested in index 500. No other savings except 401-K. Retired in 1999 at 55 years old with about $1.2 million in 401-K and $450,000 lump sum pension which I rolled over to IRA. I invested this money in bonds and only buy equities (small cap index) whenever value drop to at least 50% of its high. I made a lot of money by investing in small cap index (ticker, IWM). Because of the risk involved, I don’t buy individual stock.
In addition to opening a brokerage account, you can also invest in peer-to-peer lending firms like Lending Club. I’ve been using Lending Club for a few years, and my net annualized return was 6.02% percent last year. Picking the right investments is easy since the platform offers automatic investing, but you can also pick your own notes if you're brave and want to learn the best ways to leverage the Lending Club platform.