My wife was teaching private english lessons for a time. It seemed that she had the best results just from putting up signs around the neighborhood, at kioskos, businesses friendly to putting up a flyer, etc. She tried some newspaper ads too, with almost 0 results. Her clientele were mainly kids having trouble in their public school English classes, and needing some help, especially last minute help before exam time unfortunately. If it were me I'd try to get cozy with some public school English teachers and offer them and my current students a cash gift for new students. I'd also recommend a pricing scheme that encouraged longer term - such as paying by the month, charging for no-shows, and charging higher for that crazy last-minute help-me-with-my-exam-it's-tomorrow thing.