Hitting that Divide Button
When you subdivide your sculpture it will subdivide by 4.
Example: 1,000 polygon object will increase to 4,000 polygons. If you divide again it will increase to 8,000.
When you subdivide it creates a Lower and Higher Resolution as well as the Delete Lower and Delete Higher options. However, when you want to move in and out of subdivisions quickly, use to the shortcut keys.
Higher Subdivision: D
Lower Subdivision: Shift and D
To Add Another Subdivision: Control and D
PolyFrame (to see polygons): Shift and F
To check as to how many polygons you have on your model, look to the top at the “Active Points”
Sometimes artist have to keep polygons in mind when creating a character depending on what industry it might be used in. For the game industry, it used to be that 3D models were required to be in the hundreds for polygons and now it can be pushed sometimes into 10,000s per model. Though technology is advancing, there are still limits on most artist as to how many polys can be used on a model.
My suggestion, is to start off very simple, and simpler the better.
This was one of my first sculptures on Zbrush, working from lower to higher on subdivision levels. The photo helps illustrate how that process can be seen.