Etsy: While Etsy's popularity has declined recently, it's still a great resource for selling handmade items online. No need for complex ecommerce sites or merchant accounts or any sort of automation. The company takes a commission of every sale and charges a small listing fee per item. But many still use Etsy as their primary source of income. The best part is that you can also sell digital products such as poster designs. 
Why? Let's take a look at the numbers for a moment. Consider this: according to a report by eMarketer, digital ad spending in the U.S. will exceed traditional ad spending for the first time this year. By 2023, digital will surpass two-thirds of total media spending. Total digital ad spending in the U.S. will grow 19% to $129.34 billion this year -- 54.2% of estimated total U.S. ad spending.
One of the most important internet marketing strategies is to develop every customer's lifetime value. At least 36 percent of people who have purchased from you once will buy from you again if you follow up with them. Closing that first sale is by far the most difficult part -- not to mention the most expensive. So use back-end selling and upselling to get them to buy again:

Marketing. When operating as a consultant, you won’t necessarily be marketing your company; you’ll be marketing yourself. You’ll have to “package” yourself in a way that makes people trust you. For instance, if you’re marketing yourself as a financial consultant, ask yourself why someone would trust you with their life savings, and then figure out a way to convey that to potential clients. It might be in the form of a brochure, a portfolio, a sales letter, or all three.

Companies like Graze, Blue Apron, FabFitFun, LeTote and many others are on the rise. In 2016, it was estimated by Shorr Packaging that there were 21.3 million box subscription websites, up from just 700,000 in 2013, a roughly 3,000 percent increase. What's most interesting here are the consumer demographics. The typical visitor to a box subscription websites makes roughly $78,436 a year and is in their early forties.
Regardless if you need to earn some fast cash or we're just talking about making money in the grand scheme of things, there's an important psychology that needs to be mentioned before getting into the strategies. If you study Freud's model of the mind, you'll discover the Psychic Apparatus. It's the three-part construct in your mind that controls all of your behavior.