STEP BY STEP POSING A MODEL IN ZBRUSH
01 LOW POLY IS CRUCIAL
When you sculpt in Zbrush you are adding a large amount of surface detail onto a model that has a high polygon count. That’s how digital sculpting works. Once you have created your creature, duplicate it and hide the first copy. Use Zremesher to make it a low-polycount sculpt. Then use Tool>subtool>project to add the high-resolution detail back to the model. You need to subdivide the low poly a few times (CTRL+D).
02 LOW AND HIGH
You now have a high- and a lowpolygon model (SHIFT+D, use D to go up and down the resolution). Delete the original high-res version. Go down to the lowest resolution (SHIFT+D) and then use SHIFT+F to see the wireframe (Polyframe). Now use Ctrl+drag to mask off a part of the model. This is using Maskrectangle for now.
03 BLUR THE MASK
Now if you CTRL+TAP with your pen, the mask blurs. Any changes to the model now will be a gradual change because of the blurring effect. This is the essence of the masking technique. Use the Transpose line to adjust the head position as shown. You may need to invert the mask first (CTRL+TAP) or use CTRL+I. You can change the type of masking and use Mask Lasso to be more accurate.
04 POSE THE WHOLE BODY
Now using those techniques you can work down the whole body. Pose the head and neck first. Then the legs, the spine, the rear legs and the tail. Try and put a bend into the model as if it were swimming, as my animal is here. Put the legs opposite to each other as a real swimming creature would have. Make sure to put a nice S bend into any tail or spine to help convey movement.