Try going to our post: 20 Sites That Will Pay You to Read Books: Even though editing is not what this post is about, there are several companies that might do book editing such as Kirkus: I hope this helps and good luck on your book!
While it is important to find something that you love to do and turn it into a money making business, you do have to be cognizant of the return as you pointed out. There are many opportunities that I found and tried out that at the time seemed great. But when I took a step back, I realized that I was working a lot for very little income whereas other things I love doing brought in much more money.

The challenge I’m facing and, I know it’s a good problem, is that the SF real estate has shot up about 35% in the last couple years. I’m sure you’re experiencing the same thing! So as the net worth is rising, the yield on the total portfolio is going down. Right now, it seems the only way to increase the passive income will be to raise the rent in December and to invest some of that cash in stocks, which I’m nervous to do in this market. Current allocation:

He used "house-hacking" and "live-and-flips" to increase savings and maximize earnings, and by 2007 he and his business partner owned 50 rental properties. Save for a few setbacks during the financial crisis, Carson continued growing his portfolio over the past decade, and today he manages 90 rental properties, mostly in and around his hometown in Clemson, South Carolina.
CD Interest Income: I only have one CD account left in the amount of $185,000 paying 3%. It expires at the end of 2018 and I’ll have to figure out what to do with it. After selling my SF rental house in mid-2017 for 30X annual rent, I’m left with about $500,000 in cash after investing ~$2,200,000. The best CD today is the CIT Bank 12-month CD at 2.5%. That’s pretty darn good because just a couple years ago, such a CD was less than 0.5%. The yield curve is flattening, meaning folks should take advantage of shorter duration CDs.
Let’s continue the vintage BMW idea. Old cars obviously require quite a lot of maintenance. Many people will buy a “fixer upper” with the intention of spending their spare time repairing and restoring it. There’s a very obvious market here: a guide to restoring different BMW models. Depending on your knowledge, you could produce detailed guides for the three or four most popular models and sell them. Not everyone restoring a car will buy them, but some probably will.
Ideal locations are those that have relatively high per-capita incomes in communities that have strong local economies, low unemployment rates, and high-occupancy rental markets. Empty units cost money. Keeping them full with responsible and well-employed long-term renters will help to ensure your long-term success and continued passive income. Look for markets with job growth, Fortune 500 companies or that will soon be the home of a major new factory or large corporation as this can fuel a higher demand for housing than the present inventory can handle. The result is an increase in property value and a stable pool of potential tenants.
Acorns: Acorns is a great way to start investing and building wealth. As it turns out, Acorns will pay you $5 to start investing with them for as little as $1. That’s a 500% return, plus it’s probably time you started investing for your future. They even have features like round-up and found money that allows you to get free money from places you already shop at.
I am an English major and a herbalist with so many ideas and no extra income to fulfill them. I recently started renting my extra apartment in the attic with Airbnb. It’s amazing how fast I accumulated some money for few hours of work between guests. Now I want to persue all my dreams of opening an online herbal store, publishing my ebook of treating Ulcerative Colitis with herbs, blogs, and videos, and pretty much all of the ideas mentioned here. I will save this article as its really helpful for whomever needs some ideas…

If retirement is a goal of yours (and who doesn’t want to retire someday?!?), it’s important to learn how to start investing. In fact, funding your retirement accounts should be at the top of your list. While these accounts won’t help your immediate situation, by stashing cash now, the residual income they create should help propel you through your golden years.
Start-up costs can be prohibitive if you do not have the credit score for a loan or other financing options. Loan standards have loosened since the financial crisis and most can get some type of financing. The use of financing eats into cash flow during the early years but the strategy turns into a viable income stream after you start paying off properties.
Blogging is still going to take work starting out. That path to $5,000 a month didn’t happen overnight but just like real estate development, it build up an asset that now creates constant cash flow whether I work or not. I get over 30,000 visitors a month from Google search rankings, rankings that will continue to send traffic even if I take a little time off.

This is an ideal strategy if you live in an area where real estate prices are too high to realistically invest in, or you don’t want the hassle and expense of traveling all over the country visiting potential properties. Plus, if you are new to single-family real estate investing, letting a place like Roofstock guide you through the process is a great way to get your feet wet.
I wish I had more time to put into real estate. Given the run up since 2012, I may even be interested in selling my condo that I currently rent out. I need to get it appraised to really see what it’s worth, but I think conservatively it’s gone up ~50%, although rent is probably only up ~10% or so. I am bullish on rents going up in the future… mostly in line with inflation, or perhaps even slightly faster due to constricted credit and personal income growth which should provide a solid supply of renters. At this point, I just don’t want to manage the property. I’ll probably look into a property manager as my time is likely worth turning it into a nearly passive investment.

* I use Personal Capital to track all my finances in one place. It’s much easier to use their free software to follow 28 accounts on one platform than to log into various accounts to check my balances. They’ve also got great tools for x-raying your portfolio for excessive fees, recommending a more optimized asset allocation, and planning for retirement with their Retirement Planner.