I don’t know if you want to just play casually, or if your first harp will be a stepping stone on a longer journey. I got my first harp before I had a teacher. I called the list of teachers the harp maker gave me that day, and the one I chose advised me not to begin playing until my first lesson. Your teacher can then instruct you in the fundamentals before you get into any bad habits. If you don’t have too long before you begin lessons, you can tune your harp every day. If it’s brand new, you can even tune it a couple of times a day.
That said, if you don’t want to wait I think that many people will recommend Pamela Bruner’s books. You can find them at:
Heartland Harps
Congrats on your first harp!