In general, we use 3 different paper types: gloss and silk coated paper and uncoated white paper. Each of these paper types requires different colour separations, for which we recommend the following ICC profiles from eci.org:
Special profiles for Grayscale images with CMYK colors (to avoid unwanted color shift).
Gray in CMYK on Coated paper: coated_FOGRA39_GCR_bas.icc
Gray in CMYK on Uncoated paper: uncoated_FOGRA29_GCR_bas.icc
These profiles should be installed and used for colour separation.
RGB to CMYK conversion should be made before placing images in page layout applications.
ICC profiles should be installed or copied to C:\WINDOWS\system32\spool\drivers\color or with Macintosh: HD / Library / Colorsync / Profiles