Be sure to give them a chance to leave a message so you can get back to them. Promise a small-business owner something, and you have to follow through. Small-business margins are often thin, and a setback can be crippling. Whenever you can, include guarantees in your communications. This will help to build confidence in your target audience, by assuring them that you're as good as your word.
Direct marketing is far more of an art than a science.
As with any art, basic principles tend to emerge after years of experience. Nothing is more important than putting yourself into your market's mindset.