Basically clear mites in Nesbitts (or Konos) and mount in Hoyers but technique can vary depending on type of mites. Recipes for these and further details are in the following references. There is a section on slide preparation in Krantz, GW & Walter, DE. 2009. A Manual of Acarology, 3rd edition, Texas Tech University Press. If you don't have access to this book there is a presentation online on slide preparation of arthropods including mites by John Dooley http://keys.lucidcentral.org/keys/v3/whitefly/PDF_PwP%20ETC/Slide%20Prep%20Training.pdf