That depends on you really. What are you capable of doing? What kind of history do you have? Working online is a wide arena, full of different types of work. There's no one way to earn online. You have freelance sites out there, where you can provide your services. They have microworking sites, survey sites, writing jobs, content creation, graphic design, coding, and oh so much more.
Your best bet is to find a niche you can do, a niche such as graphic design/coding are great, because they can pay a lot. But, there are small time jobs you can do all over the web as well, albeit, they don't always pay much.
Essentially, the best way of earning profits, is by finding a service you can produce, that will yield you better profits.