SEO WritingA good way of generating writing samples is to take up SEO writing though the pay is very low but you can generate lot of samples as the topics on which SEO writing is done are of a very wide range.
Do a Google search and look for freelance writing jobs. You could volunteer. Create a profile in a social networking site like Linked in or Facebook. Even Twitter offers lot of writer job links. Just stay active on these sites. Create your blog. This gives you good writing practice and also serves as a writing sample. I would suggest that you start your blog on a niche you have knowledge of and are comfortable writing about.
ReferencesWhatever work you do, ask the client to write a small testimonial for you. Try to get a link to all the ghostwriting assignments you do, or assignments that do not give you a byline.
DeadlinesMeeting deadlines is an essential part of freelance writing. Most clients who ask you to write articles for them, want them in a short span of time. While I would suggest you to avoid clients who ask for 5-6 articles in a day, or want you to spin articles for them, if you are hard pressed for money, you could also attempt those. Avoid clients who pay $4-7 per article though. It does nothing for your portfolio or self-esteem either.
PersistencePlease remember nobody makes a name or earns a good income overnight, patience and perseverance is the key. Patiently build your portfolio and contacts. After you have built a good client base, you can happily bid that day job goodbye.
Last word on this Good Luck!