In other words, the place to start is where you are and where you are depends on your unique circumstance. EU citizens have different options than Thai citizens. Graduates of a US university have different options than those of a Chinese university.
Good luck.
I'm Brazilian, working to a American company as Ruby on Rails developer, I don't have any qualification, but I'm good with Rails.
But I would suggest just searching around on the web for companies doing work in fields that you have experience in or fields that interest you. Go look at their website and see if it looks like a group you want to work with. Then check to see if they have any open positions. If they don't have anything you'd fit well, but you're confident you have something to contribute, contact them anyways. Write them a cover letter saying that you think you can contribute something they haven't thought of and send your resume with it.
edit: Brudgers raised the really important point that there are many practical considerations to make before contacting companies. Figure out what's possible first.