I, personally, wouldn't (and don't) use those sites to generate web copy clients.
The quickest way to get started is by building business relationships. If you present well face-to-face, have some business cards printed and become visible wherever businesses in your target market hang out--chambers of commerce meetings, business networking socials, meetups, whatever...
If you don't do well face to face, then start scouting some of the small to mid-sized web design firms in your area. Meet with them and get to know the people working there. Present yourself as a freelance copywriter willing to be a value-add for them.
Talking to design companies of various sizes, I've discovered that many don't have copywriters on staff or even offer it as a service.
I can't tell you how often I've seen web designers roll their eyes, and throw their hands up in frustration, over projects that have been delayed because the clients are slugging away at the copy themselves.....
And frequently when the design companies get the client-generate copy it tends to be horribly amateurish.
So start there. That way you can determine the price for your services, rather than get stuck in the $10 per article hell that's bringing this profession down.