Have you heard of a "get-paid-to" site? These are increasing in popularity, particularly among the younger generation. You can earn money by subscribing to newsletters, playing games and completing surveys. Particularly if you do not have a marketable skill, this may be the easiest way for you to earn money online. However, make sure you find a reputable site to work with.
If you plan on making serious money online, make sure you've got the right equipment for the job. There's nothing more frustrating than trying to complete a job and your Internet times out, or is so slow that you miss a bid or other opportunity. Have the necessary equipment and make sure you're software is up to date too.
Photography is a growing business. If you like taking pictures, and you are good at it, you could make money selling those pictures online. Look into companies like Shutterstock and Fotolia, which are stock photo agencies. They make it easy for people to earn a little extra money by taking pictures.