The easiest way to do this is to create a profile on a site such as Elance. Once you've done so, you can immediately begin bidding on jobs from clients around the world. This is where I got my start as a freelance writer after college and my first job was for a start-up in Singapore.
However, the vast majority of the jobs posted on these sites offer very poor pay. It's a good place to get experience, but I wouldn't advise relying on it for any kind of serious income.
Another useful site is Flexjobs, which lists telecommuting jobs, though they charge you for the service.
Finally, there is always the old-fashioned direct approach. Find a client you'd like to work for and reach out to them with a proposal and examples of past work. If your experience is anything like mine, you'll be rejected quite a bit, but you'll learn a lot about dealing with people on the way and when you do get work it will pay much better than about 99% of projects found on bidding sites.