In order to really improve these models, you need a more in-depth knowledge of anatomy, proportion and posture. You won't necessarily acquire these skills though modeling. Your best bet is to do a lot of figure drawing. Drawing is a much faster medium, so it will allow you to iterate on your skills much faster.
It's good that you're doing some drawing already. Be sure to use reference though and not just draw from the head. If you draw from the head, you don't learn anything new about anatomy, you just solidify what you already know. It's best to draw from a real model if you can, but a good alternative is to get a large mirror…
I had this whole rant on anatomy and proportions, but others have already covered that, so I'll skip it. The other thing I would suggest that will help a lot in Z-brush: Start low. Start as low poly as you can, and don't move up until you absolutely have to. Get every ounce of detail out of a subdivision before you divide…
All right, it's late and I've been drinking, so I'm gonna run through this quickly. -Texturing Only 3 out of 15 of these have any sort of texture. And the ones that do only have big chunks of primary colors and no real material definition. You really need to look into working with spec and gloss maps since that is pretty…
In regards to learning to draw and studying anatomy, you need to gather some artists that you like, analize their drawings and compare it to yours (be a real critic to yourself). Here are some drawings from Jana Schirmer and Kevin Wueste - notice the "study" quality of them - every line has a purpose and nothing is…
As DemonPrincess stated,Anatomy is one of your best bets.You'll be surprised at how much your character's overall look and self pops with the correct adjustments.Look at some of the Masterworks out there.Michelangelo,DaVinci,etc. I recommend Scott Eatons courses as advice.I recall myself saying "Oh,I'll never be able to…
The guys above have some very good advice. I would add that it seems like you are using the exact same basemesh for each female piece, which is a huge handicap when it comes to learning. I might be wrong and I apologize if I am, but the anatomy is apparent in the fingers and general shape, and the topology all reads the…