Fellow speaker,
Your current customers are your best marketing sources. Listen to your current customers and find out what they like about your speaking. Then use those words to market to other people. For example, if you ask someone what they liked about your presentation and they said, "I love the way you take complex ideas and make them simple and easy to understand," you market yourself saying, "I take complex ideas and make them simple and easy to understand."
Out of the mouths of customers,
Tim