If you're using the 30 second exercise, you're not supposed to even use guidelines. Just draw it as you see it, proportion is not really the point, although they will naturally get better as you go along. If you can draw even the pose of the hand in that time, then you've become really good. The main point is to understand by experience how muscles bend in different perspectives, so when you draw on your own without reference, you'll naturally remember it and be able to make up your own poses. For example, one thing you'll improve really quick is how the shoulders bend, and its a small thing that makes your poses much more natural.
As for perspective, that is a whole other can of worms. You can learn how to do heads looking up and have the body parts in different angles fairly quick, but doing a whole picture in an odd perspective like you wanted is hard. After almost 6 years of drawing, 4 casually and 2 seriously, I still don't like to do it. The basic idea is to find a vanishing point and then draw the whole rest of the picture inside guidelines that originate from that point. This can turn into a mess very quickly and that's the simple perspective. There's other types of perspective that can have up to three vanishing points. You can search for some tutorials online, but this is something I recommend buying a book for.
I'd leave you with some tutorials, but all of the ones I found online suck compared to books, and almost all of them focus on architecture and don't show how figures work inside the guidelines. Even a small magazine that has 10 pages dedicated to it is better than those tutorials. I'd scan it, but its in Portuguese, and so is the book I have. Best thing to do is to check if your library has a book on it, and figure out if its something you want to focus on now or do it later when you have more experience.
