Hey man, I really think you have something brewing here. I don't know the best practice method out there, nor does anybody else, but there is one thing I can tell you. Always try to understand why you do some sort of exercise. The books give answers, and you can find answers all across conceptart.org. You should be content with an answer and believe in it. Confidence is really one of the biggest factors to drawing.
On the subject of drawing from life, I believe it's pretty important. Andrew Loomis: Successful Drawing is my current eye-opener. He talks about the fundamentals of drawing, but that is not restricted to the perspective that is also in the book. Drawing from life is one of the easiest ways for you to to portray some sort of message. Always try to find something interesting, whether it be the subject you are drawing or the composition. And of course, if you want to get into drawing from imagination, look into his first book called Fun with a Pencil. It is underrated but it is a great way to open up the creative pipes. Do not copy the drawings but try to do your own. Try finding some inspiration from any of the many mediums of entertainment if you have to.
Good luck man!