Writing and publishing an eBook has become a widely popular means of earning passive income in recent years. eBooks on non-fiction topics like online marketing, business development, career advice, and the like are especially successful. While fiction eBooks are also good sellers, the market for them is much more competitive as compared to non-fiction ones. Once you've written an eBook, you can put it up for sale on platforms like Amazon's Kindle Direct Publishing or Apple's iTunes Connect.
6) Always Remember That Everything Is Relative. The best way to determine worthwhile passive income streams is by comparing the likely return (IRR) with the current risk-free rate of return. If I round up, the 10 year bond yield is at 3%. Any new venture should thoroughly beat 3% otherwise you are wasting your efforts since you can earn 3% doing nothing.
Capital growth in your portfolio can offset the eroding effect of inflation.  But any capital gains that exceed the overall inflationary effect can be drawn off to augment your portfolio income.  Of course, you must first generate those gains by making thoughtful investment selections.  While allowing strongly growing assets to keep doing that, it is prudent not to allow them to become a dangerously large part of your portfolio lest they go off the boil.  So if you selectively trim profitable positions along the way, you can boost your income.
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.