I secure the bulk of my writing work through querying various publications. I study their guidelines and past issues to find a topic that may be of interest to them. I also write resumes and do some business writing which is usually generated through some free classified ad boards that I post on. I have probably secured about a handful of assignments through answering ads on craigslist.org. Securing assigments and anwering writing requests from craigslist (or similar venues) is an ongoing task so it cannot be one of those things that you do once in awhile. Although I have signed up with elance.com, I have not actively tried to bid on anything. Hope that helps.
–Late Night Writer