Hi,
Here is some of my 3D modeling workflow in ZBrush that may be helpful. 
i first started with a 3d concept model i made a while ago but had little appeal and i used very little planning for it.  i then added an idea for concept ontop  of the sketched model giving a better indication of direction.  The little notes are guides so in ZBrush i can begin addressing the notes.
Then i blocked in major portions of the model trying to get proportions similar to concept.  I used mostly the insert brushes and i tried to work on as low a polygon counts as i could (zremesher, halfing the poly count).  (also is shown is the use of the zspheres in blocking out the back legs that i posted in an earlier post).
Then i sketched over the blocking refining the concept some more and making it a little easier to develop in ZBrush.
Then i worked the broken up pieces some more before I then merged them and worked on them some more using smooth, clay buildup, damian standard, move tool and a couple other brushes.
The clay buildup i used much more in the later stages.  (from the 
blocking to the more refined modeling took about 2 hours,  the more 
refined 2D concept sketching took about 40 minutes)
And here are some ZBrush hot keys i used that i found very helpful.  
hotkeys:
n show all subtools
u     intensity
o     focal length
s     size brush
shift    smooth
shift     snap ortho view
b     enter brush mode
alt     pan
ctrl     mask,  click invert mask,  click off remove mask
hold shift last circle move     scale
q     exit move mode
r rotate
b,f,a     brush flatten .. (the b,f,a means first press b then let go then press f then let go then press a)
b,c,b    clay build u
b,m,v  move tool
b,m,l    lasso mask tool,  b,m,k  mask pen
b,d,a    damian standard
b,i,w    insert sphere
b,c,i     clip curve
Hope this was helpful.
cheers,
-Nate 




