These steps make it much easier to retopo a model.

1. Snapping

snap

  • Set Face snap mode
  • Set Project Individual Elements mode

2. Mesh Tools

In the Tool Settings of the edit mesh mode, set the tools to "auto merge" and set the merge distance to something fitting your model.

automerge_vertices

3. Active Mesh

To eliminate z-fighting between source and retopo object, set the retopo object to "In Front", found in the Viewport Display menu of the object properties.

set_in_front

Here you can also set your model to Wireframe display and set a viewport color for your model.

4. Modifiers

These modifiers will help you with precision and workflow:

  • The Shrinkwrap modifier improves the precision of the final mesh. You can set an offset, if you have issues with z-fighting.
  • The Mirror modifier mirrors the geometry and merges the edge vertices to get a closed mesh.
  • Alternatively to the Shrinkwrap offset, you can use a Displacement modifier. This way you can't forget to delete the offset before applying the Shrinkwrap.