Unfortunately we don't have specific instructions for every application out there (there are just too many) and settings really depend on what you want to do with it. We do have some general recommendations for preparing models for best use in Dimension here:
Supported 3D model formats and content
If you have any .obj files that fail to import you can e-mail them to tickets@adobedimension.com and we'll take a look. As mentioned by Kat, Dimension is a relatively new app, so we're still working on the robustness of the importer. Since .obj is an open format there are many variations of it, lots of edge cases we run into. The majority should import without any specific settings though.