The thing that bugs me is... well everyone tells me to practice. I'm okay with that, I love fiddling around! But, I dont really know where to start. I'd like to be able to draw everything, from humans, aliens, landscape and my mind. Sadly I don't know where to start. I thought about buying a book, but I'm not sure I could find one specifically aimed for digital drawing.
Start with basic human anatomy. Pick up "Drawing the Head and Figure" by Jack Hamm. It's a good basic over view of anatomy for a beginner. After that I'd find a good anatomy book, like "Atlas of Human Anatomy for the Artist" by Stephen Peck. Then find a good book on perspective, I like "Perspective! for Comic Book Artists" by David Chelsea, which is something you should pick up once you're confident with drawing bodies.
The medium you're using (pen, paint or digital) comes second to the basic skills that all artists need to make a convincing piece of work. Also, try finding some live figure drawing sessions in your area, and if you can't find any, go out with a sketch book and just draw people you see. You just have to keep drawing no matter what!