There are different routes you can take but here is a exsample when wanting to retopologize somthing build from zsphears.
1: Sub-D lev 1, Use mainly the move tool to build basic volume.
2: Sub-D lev 2, suclpt basic form, keep adding more form smoothing in between and re working over the areas.
3: Dont go for high details, just basic detail to identify clearly the mouth, eyes, ears and nose.
4: Sellect the Zsphear tool, then go to rigging menu and sellect mesh.
Click on edit topology from the Topology menu below the riging text menu. Clear all masks. In adaptive skin text menu, set the density high or low to preview your mesh at different Sub-D levels. Pressing the A key will preview the mesh, A key pressed again to go back to yur topologizing.
5:In the Projection text menu click on Project. Next time you press the A key for preview, the details will project. Make sure your adaptive intencity is set equal to your mesh highest level when clicking the Make adaptive skin button.
6: when you have done this a new model is made in your tools. The tools will have Skin as art of its name. When you clickon this your have your detail projected to the highest level with all lower levels of Sub -D in tack.
If the projection makes a messs, either make sure you have tryed to set the Projection range to a minus level like -0.01,or make sure your new topology is complete and lines are connected where you think they should be.