Ok, from the perspective of a brand new harp student (that’s me!) who has now been playing for 5 weeks I have to say that the book my teacher started me with has made it a very fun experience since it is basically a sweet book of songs that are very pretty and fit very easily under my fingers. Even in the first week I felt like I had made very fast progress and was actually playing music. I think that is very important, learning a new instrument is daunting and I imagine most people give up quickly because they feel it is taking too long to progress to playing music and sounding nice.
The book is Midnight Fairies by Kelsey Hughes. I think you can order it online and have it shipped or download it from Sylvia Woods website (not positive, I bought mine from my teacher)
Also, when learning other pieces my teacher would post mp3s of the music for me to play along with and practice, I found that VERY helpful and fun.