I'd say start with Youtube -- lots of free videos on longarming and tools used in longarming.
I think the Quilter's Academy series of books is for beginning quilters -- sort of taking them from cutting fabric through piecing and layering, then to quilting. I think it covers quilting on a domestic machine (which is how Harriet Hargrave quilts); didn't know it even covered quilting with a longarm on a frame.
In my experience, unless you have bought a longarm system from a dealer comlete with lessons, a lot of longarming is sort of teach-yourself by means of trial and error. Youtube videos gave me a starting point for loading a quilt.
What setup do you have?