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.
Amazon offers a service called Fulfillment by Amazon (FBA), which can be extremely useful for arbitrage sellers, or others selling their own products. If you opt for FBA, Amazon will store, pick, pack and deliver your products. That means you can scale your arbitrage business quickly as you don’t have to store products in your own home or waste time with postage.

Many work-at-home companies hire you as an independent contractor as opposed to an employee. That means you are responsible for submitting your own tax payments. Taxes won't be taken out of your check like you are probably used to. It's so important that you keep good records of your income – and expenses. I highly recommend Quickbooks Self-Employed.
Mechanical Turk is Amazon's take on micro-jobs. These are small miniscule-jobs that you can do for other people, which they call HITs, or Human Intelligence Tasks. These are super simple tasks that anyone can do. Some examples are listing off some URLs with certain kinds of images for one cent, or recording a few phrases with a microphone for 6 cents.
If you offer freelance services or have a physical services business, then creating a blog is a must. On your blog, you can write about the services you offer and how they will benefit your clients. Importantly you can add a ‘Services’ page, outlining the services you provide, what they include, and any other important information potential clients may need. This is an effective way to promote your services, generate leads, and increase your revenue.
Take it seriously. Yes, you’re applying for an online job. Yes, you can do the work in your underwear, but that doesn’t mean it’s not a “real job”. You must treat it as such or they aren’t going to treat you as a serious candidate. You aren’t the only one who wants to work in their underwear. In fact, the competition online is likely higher than it is in your local area.
If you’re a skilled worker in a specific niche, like marketing, design, or software development, there are specialty marketplaces that cater just to you. These are amazing places to make money online as you know that the people visiting them are looking specifically for the skills you have. Check out places like 99Designs or Dribbble for designers, Cloudpeeps for marketing and SEO professionals, and TopTal, Crew, or Gigster for high-level software developers. Once you've built up your development skills, you can begin building a brand for yourself as a higher-value consultant and start charging brands for larger projects like implementing an entire WordPress security overhaul or migrating a website from http to https. 
×