There are many people who won't leave messages on voice mail. Don't try to do business on the phone with kids screaming or playing noises in the background. Don't use a tape answering machine, they scream amateur. Get connected to professional voice mail or invest in the new answering machines that sound like voice mail. Have a separate phone for business, always answer professionally and never let kids answer it.
Return calls promptly.
Network by joining your chamber of commerce and also by joining any professional trade associations for your industry. Be sure your business cards, letterheads, brochures and other printed matter look professional. Many potential clients will judge you not by where you work from but by the image you project. Dress professionally when you meet people. Casual around the house is fine but never when you are doing business in person.