One of the most beautiful and exciting qualities about blogging is that you can create a blog that deals with any subject area that you are either knowledgeable or passionate about (and preferably both!). You can write about personal finance, careers, real estate, getting into business, technology, cooking, travel, personal health, or just about any topic you choose.
If you're serious about making money online, start a blog. Blogging is one of the easiest and most sustainable income sources. As long as the blog is setup the right way, in the right niche, with the right content targeted at the right audience, and the offer is complementary to the content, you could make a tremendous amount of passive income from a blog.
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. 
In 2017, there were almost 90 million pet dogs in the US. Which has opened up a huge opportunity to make money online as a dog watcher or sitter. Specialized sites like Rover or Care.com connect pet owners with pet walkers, sitters, and boarding houses to help look after their best friends when they’re at work or on a trip. If you’re an animal lover, you can make extra money and get to spend some quality time with a furry friend.
You'll also need ecommerce software, fulfillment software, worry about warehousing, customer service, refunds and so on. But that's not all. You'll also need traffic. Think search engine optimization, Facebook ads, and other social media campaigns. Sound like a lot of work? Sure, it is. Especially if you do it all on your own. You could opt for Amazon's platform, which might be the easier route. But, then again, at the end of the day, this is a serious business, which could produce significant profits. So you're either all in or you're not.
Whether you have a website or are still dreaming up ideas for a blog, you can also look into affiliate marketing. With affiliate marketing, you partner with brands and businesses within the content of your website. If you mention a product or service, you link to that produce or service using a unique affiliate code you received when you signed up for that particular affiliate program. From there, you’ll make money any time someone buys a product or service through your link.