Regularly post in the forums
Don't just post everwhere. Post in places related to writing such as DP's copywriting section. This way things stay relevant. Furthermore, people will see your signature and want to know more about you. This is especially true when you answer someone's question. They see you are a helpful person and want to know more about you. It´s called giving to the community.
Give instead of taking
Sure, you could easily make threads or post services but this won't do any good. It's better to offer something unique within your services. Give something the client wasn't even expecting. I remember my first gigs on Fiverr that I had as a writer and I would often throw in a freebie. Clients really appreciate this and they will leave you good reviews in return.
Spread out your services
Focus on two different places to begin with. For example, you could use DP and also Fiverr to sell your writing services. There are tons of places online. Each client is different when it comes to shopping for articles. Some prefer chatting with someone who is established and has been on the forum for while. Others just want a good deal, despite if that person is new or not.
Build a portfolio
The majority of clients that you write for will be posting articles on their blog. Ask if you can link to their blog to show off your work. They will be getting free traffic and you will be showing off your portfolio. This is clearly a win-win situation here.
Write about topics you love
The best type of article is one that is written with passion. Those are the ones where you completely lose track of time, focusing on the article only. You may have traveled outside of your state to go to New York and want to write about your experience. Put together a few different articles which focus on different places within the state that you visited. You can always save these in your own article library. Offer them to people who have travel blogs. Better yet, you can even put them in the article marketplace of DP.
Always be available
Try to be available on Skype or e-mail. Most clients will want to reach you for an urgent project and discuss the details. Some are busy and have 9-5 jobs so they can only contact you at a certain time. Others also work in freelancing, often using you to outsource the work so they may be extremely busy with other clients.