It’s hard to get paid without customers. 

That’s true no matter what industry you work in. For writers, finding customers might seem less intuitive than for people who sell goods or other services — but in truth our market is all around us. Here are five broad categories of sources for leads to get you started in writing professionally.

1. Writing Market Guides

Writer’s Market, Wooden Horse Database and Herman’s Guide are like phone books (remember phone books?) for writers. They list publishers, agents and editors who pay money for good writing. Unlike most of the free listings you’ll find, these for-pay editions offer insight into specifically what each listing is looking for. Wooden Horse even includes the editorial calendar when it can. These cost a bit of money, but are among the best resources for book and article writers.

2. Shelves

Shelves at the library, your favorite book store and the local newsstand all have dozens of magazines that pay people to write for them. Shelves at the hotel have brochures written by companies that may need somebody to write another. Scan shelves of literature everywhere you go, and figure out how to turn some shelf-dwellers into clients. One of my favorite sources is the coffee table at my doctor’s office. Every time I go in, I find a new magazine I’ve not sold to…yet.

3. Contacts

This is the Best Source Ever. People you know who need writing and can pay for it. Not only do these people give you money, but they’re soft touches for more work in the future. The overwhelming majority of my writing income comes from people I’ve met by getting an earlier job from them, chatting at a conference, or random acquaintance. Sometimes you have to push a wee little bit, but just about everybody you know will need something written beautifully at one time or another.

4. Them Tubes

The Internet is full of the written word — and it’s easy to tell which of those words were written by a professional. Google’s new Penguin update is making it even more important for those words to be top-shelf. Start with the blogs and sites you already frequent, by offering a guest post after commenting on a few blog entries. Move on to new blogs about topics you understand. Meanwhile, don’t discount the value of job sites like Craigslist, Freelance Daily, Associated Content (Now Yahoo! Voices) and Online Writing Jobs for getting those first deals.

5. Social Media

Although it’s technically part of the Internet, social media deserves a mention of its own. Used right, these sites combine the global reach of Internet sources with the personal touch of contacts. For professional writers, LinkedIn is probably the most robust source of leads — but the new “authorship” ratings from Google mean you should be up on G+ as well.

Any sources I’ve missed? Any personal experiences, recommendations or ideas? I’d love to hear what you have to say about them. Tell us all in the comments below.