Your best bet is to email/call up editors and constantly surf the net for opportunities. Make Search Engines (google, yahoo) your trusted lieutenants and use them to help you seek, search and finally apply to advertised or possible opportunities.
If you find good websites you could write for, look for submission guidelines or send in your query. A query letter is not a waste of time. On an average three out of every five will elicit some kind of a response that will take you forward.
Though it is usual practice in established writing circles not to start writing till an understanding is reached, you the newbie can take no chances. So, till you have sufficient work, give them what they've asked for, quickly, whatever the subject, or send them something you have already written. Odds are that they will use it and pay you with a nice "Thank you for your submission' letter or not at all, but if rejected or if you don't hear from them ever again, which is highly likely, don't lose heart. Move on. Just keep those articles as ready-reckoner samples for later use. Stockpile them in a folder for the future, to be sent on to other editors who may seek samples of your written work.
If they are freelance writing markets, narrow in on the popular ones. Subscribe to their newsletters. Most of them are free. It will give you a fair idea of their reliability. Generally avoid those that promise you the moon. Look for those that seem sincere. But do not subscribe or pay for anything till you are sure of a website's credentials. Also, remember to check out the various published lists of dishonest and fly-by-night operators often. Soon you will be able to sift the wheat from the chaff.