In my early years of studying to enter the field of education, I did so with the intent of teaching Spanish to native English speakers. Since then, I have not once taught this subject to this demographic. Nevertheless, I did enjoy the preparation for it, and the student teaching experience that crowned these efforts. The students I worked with (attendees of both public and private Christian schools) were great fun and full of enthusiasm.
One great resource that I was introduced to during my time in the local public high school was a series by the BBC called Mi Vida Loca. You can find that here. It is a series of interactive videos that can be shown in Spanish or English, with subtitles or without, in which the learner goes on a trip to Spain and has to find his or her way around the city following the host Merce. This is a great tool for beginners to get their feet wet, while being fun and engaging.
This is also a tool I recommend to those adult learners who express an interest in Spanish because it steps you through asking for directions, negotiating prices, ordering food, and other everyday situations in which you might find yourself. The vocabulary taught is both simple and practical.