First of all, person/company needs to find out if this product even required RFD because not all product required RFD submission. The necessary step to take before submitting RFD with a better understanding of how the product works and then contact OCP (Office of Combination product) if you have question about type of information should include in RFD if not sure enough; from my point of view correct me if I am wrong, this step will help you minimize RFD rejection. The RFD should be submitted before filing any investigational or marketing application for the product. This will avoid expending unnecessary time and resources.
US FDA has three key concepts it uses in the regulation of combination products
• Constituent parts retain regulatory status and duties
• Combination products are a distinct regulatory class
• Comprehensive, effective oversight without undue redundancy
All other necessary steps to get FDA approval of a combination products are well described by jvv6 and djr32.
Reference
http://www.fda.gov/CombinationProducts/GuidanceRegulatoryInformation/