The early bird gets the last-minute appointment. "Patients who cancel often call at night or very early to leave a message with the answering service," she says. "They don't want to speak to a person because they feel guilty." She suggests you call the minute the office opens to nab a cancellation.
If that doesn't work, you should say, "I can come in Wednesday at any time." Leaving it open-ended shows that you're serious.
One last thing: "You know what will not get you in here? Not being nice to us," she says. "Be friendly, and we'll work our butts off to accommodate you."