CMYK profiles are device dependent – each profile describes a specific press and paper type. You need to discuss which profile is most appropriate with your printer.
There is no "generic" CMYK profile that will suit all press conditions. However, if you need to convert to CMYK but haven't been given any information about the press type then the safest profile to use is ISO Coated v2 300% (ECI). This profile is used for the highest quality magazine printing and CMYK images that use this profile are fairly easy to adapt for different press conditions.
You can download the latest European Color Initiative profiles from the ECI web site.