This book is about as basic and ground level as it gets, covering essential things like casting circles and calling on the four elements. I went through about three copies of it while i was in prison, and still to this day I find myself leafing through it every now and then. And if you really want to dig deep, this book is the first in a trilogy, so you could go on to the other two. I can't recommend these books enough, as well as one other she's written, and we'll cover later.
She has a very conversational writing style - like you're just sitting in her kitchen talking as you grind herbs swap techniques. If you've never in your life read one single book on magickal technique, then this is the one you should probably start with. I think it's probably just about perfect for anyone age 15 and up.