Man, I dunno.
I shelved out my precious money to buy Zbrush 2018. And decided to do something with it. I watched a few tutorials and read some documents. The real roadblock is that I need to conceptualize first in 2D thoroughly. For this practice, I did not prepare any sketch and improvised the design straight out of my head.
Fortunately for me, it's more fun than I expected. And I also realized that few people utilize most of existing functions anyway.




The rendering was done with Modo. As you see, I have no clue how to properly retopo the zbrush mesh.

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As far as retopologizing and making game models, that's a bit to learn and practice but all the information is out there -- a lot here on the polycount wiki.
In order to get accustomed to the tools and also find out whats all in there, you might keep filling out this character -- doesn't matter where it goes you can just make it up as you go -- and inevitably you will run into situations where you will think, "this would be easier if I could do something like this..." and then you search for whatever that idea is, and most of the time you are going to find there is a tool just for that purpose. Not the fastest way to learn, but it's a very fun way and what you pick up will stick with you more than just following tutorials or reading documentation.