One of the best places to sell unwanted personal possessions is Decluttr, a website that buys used items directly from consumers. Unlike trade-in marketplaces such as Gazelle and auction websites such as eBay, Decluttr doesn’t act as a middleman between buyers and sellers. Rather, it’s best understood as a bulk buyer: an enterprise with deep pockets and an unsatiable appetite for used consumer products.
If you’ve got a way with words and expertise in a niche, there are plenty of sites that will pay for articles and content you write. Think of the sites you read regularly. What can you contribute to them that would be interesting? Research your niche and then look for ways to pitch articles. Many sites will simply have a submission or contact link in the footer. To get started, check out my full guide to becoming a freelance writer on the side and then submit your articles to places like Instash, Listverse, TopTenz, A List Apart, International Living, FundsforWriters, and Textbroker.
Once you have that problem or need nailed, the next step is to validate that idea and make sure you’ve actually got customers who will pay for it. This means building a minimum viable product, getting objective feedback from real customers, incorporating updates, testing the market for demand, and getting pricing feedback to ensure there’s enough of a margin between your costs and what consumers are willing to pay.
Find a profitable niche. Starting with your interests, write down as many niche ideas as you can. Think about topics people might search online. Ideas include passions (like surfing or body building), fears (like spiders or speaking in front of crowds) and problems (like getting out of debt). Do keyword research to see it others are interested in the topic. Find out if a domain name is available that matches the keyword 100 percent. 
If you're ready to enter the ecommerce fray, you could sell your own stuff. Of course, along with selling your own stuff on your own website comes a whole slew of both responsibilities and technical configuration and requirements. For starters, you'll need a website and a hosting account. You'll also need a merchant account like ones offered by Stripe or PayPal. Then you'll need to design that site, build a sales funnel, create a lead magnet and do some email marketing.
If you’re a fitness buff and have the right combination of charisma and business sense, working as a part-time online personal trainer can be both physically and financially rewarding. Once you build up a reputation and client base for yourself, it could easily turn into a full-time endeavor for you. Check out this interview with several fitness blog owners who are making a living online, from MonetizePros. As well, I'd recommend checking out this resource if you want to take this business idea seriously and get started with a business plan for your personal fitness trainer business today.
Now, making money online should seem like a pleasurable activity. Why wouldn't we do just about anything to see things through, since it would be a major source of pleasure, right? Wrong. In the beginning, like anything else, we might get really excited about it. We might also set our hopes very high. But that all comes crashing down when we begin to fail.