Do you know who your best source of clients is?
You should. Your best source of clients are your current--and former--clients.
Clients who you've worked for before are an overlooked marketing tool for freelancers. When you've done a good job for an editor, private client, or corporate contact, he is (presumably) happy with you and your work. That means he's a potential walking advertisement for you.
So let me ask the tough question: do your clients send potential clients your way? Do they think of you when someone they know is looking for a writer? Have you even asked your clients to refer you or give you leads?
If not, why not?
I suggest you get in the habit of asking your regular clients for referrals. I don't hit up a regular editor for work all the time, but when I'm getting slow, I'll mention that I'm actively looking for new work and ask her to keep me in mind for referrals. When I complete an assignment for an editor who's new to me (and she's accepted it), I'll ask if she knows of other editors looking for freelancers. For a ghostwriting client, when I finish a book, I'll ask if he knows of any other would-be book authors looking for a ghost.
No, I can't expect my clients to do all of my marketing for me. Depending on where you are in your freelance career, and the type of work you do, you can expect to spend 20 to 90 percent of your time marketing your business. But looking to satisfied clients for leads and referrals should be one of your go-to freelancing strategies.
**I'm excited to announce that in June I'll be participating in the 2014 Freelance Success/Word Count Blogathon. I commit to blogging every day for 30 days, along with 50+ bloggers on a variety of topics. I'm already putting together a list of topics but if you've been wanting me to cover a specific topic here (and I'm already considering the ones readers suggested here), comment below and I'll see what I can do!