You've got the right idea, working from big to small and getting the whole pose in place. When you're brand new to this, the only thing to do is keep a steady pace and watch the pile of drawings grow. Eventually you'll have quite a lot of them and you can evaluate your current work vs. the old stuff.
A good habit to build is making one deliberate line and leaving it alone. In a school setting, this is part of why vine charcoal is used. But the broad side of a pencil can be used to the same effect, or markers if you're feeling up to it. The idea is that quick drawings like this aren't really about drawing fast so much as making efficient decisions. The extra time thinking before making your mark is made up for by never having to scribble or draw back over.
While the most important part is the actual hours spent drawing, you'll also want to be studying anatomy and figure drawing from one resource or another. This gets to be a contentious topic with people having strong feelings about their favorite artists and authors, so take your time looking around. Andrew Loomis wrote a series of books during the golden age of illustration that are probably the most popular. Personally I'm a fan of Gottfried Bammes for his geometric simplifications of the human body (some people find it too "stiff"). And for the classical, 19th century approach, there's Paul Richer's Artistic Anatomy, which every book since owes some debt to.
Keep it up and don't forget to have fun.
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