How much do you know now? Have you taken a basic class or gotten instruction from your dealer on how to load a sandwich and basic operation of the machine? That would be the first thing I would recommend.
After that, what I did was just dive in and go for it. Do not be afraid of your machine. Do not be afraid of "ruining" something. Fear paralyzes you and keeps you from reaching your full potential in anything but especially in longarming. Also I drew a LOT. I wanted to master feathers so I spent evenings with a big pad of cheap newsprint and pen and drew feathers going in all directions. You can also use a white board.
For me, drawing translated well to longraming and drawing gave me muscle memory as well as thread path memory. I can now quilt feathers as easily as signing my name.
If you get the opportunity try and take classes at the big expos that offer hands on work with longarms. Pick and choose the classes carefully as most run over $100 a pop for a big name teacher. I took one with Karen McTavish about 9 months after I got my longarm at MQX. Money well spent IMHO.
I am a book junkie and I have several books by longarmers like Gina Perkes, Judi Madsen, Angela Walters and Karen McTavish. I also subscribe to Machine Quilting Unlimited. Great publication for both longarmers and DM quilters.