High to low process

If your object was sculpted in another program then you'll need to export a copy of your high poly mesh from your sculpting program. They key is that you don't want to export the highest level of the sculpt. You want to export the lowest level possible while retaining the shape of your mesh.

Related videos on the subject.
Maya 2014 New Modeling Tools - CGMeetup.net

In summary...

  1. Import the high(er) poly mesh into maya.
  2. Select the high(er) poly mesh.
  3. Click the "live surface" snapping tool on at the top of the interface. The name of your imported mesh should appear next to the icon.
  4. Make and select a low poly mesh object.
  5. Turn on the modeling toolkit (Mesh Tools > Show Modeling Toolkit).
  6. Using the "quad draw" tool you can place vertices on the surface of your model.
  7. Use Shift-Click to fill in the space between four vertices with a polygon face.
  8. Remember you can easily adjust the position of mesh elements at the same time while in this tool, and also that you can relax the points of your new surface by holding down shift while over a vertex.