List your Twitter handle (account name) on your business cards, résumé, and LinkedIn profile.
I'd add that you should also list it on your business web site and wherever else your business profile appears online, such as directories of those in your profession or members of a professional association.
I'm on Twitter all the time, mostly for business purposes, but it hadn't occurred to me to include my Twitter handle (@KOKEdit) on my business cards or résumé, even though I list it on my LinkedIn profile and on my web site. Including your Twitter handle on all of your project-seeking materials, including e-mail signatures, is a great idea because potential clients can then follow you on Twitter and get a sense of who you are, what your outlook on work and your profession is, and how you think.
Take a look at how I've incorporated my Twitter handle into my résumé (near the top of it).
Maybe including your Twitter handle on everything you can think of seems like a minor detail, but these days, it's important to take advantage of every possible tool to help potential clients to find you.
marketing social media Twitter freelance copyeditor copyediting publishing EditorMom