The FDA regularly issues drafts of guidances. What most people do not know is that anyone may comment on these drafts. Normally, the FDA also allows the public enough time to do so.
When the FDA publishes a new guidance or revises an existing one, it announces its intention in the Federal Register. This is also accessible on the internet. As soon as the announcement is published, the period for comments begins.
The procedure is described in detail on the page How to Use Regulations.gov. It explains how to search for documents.
Comments are typically submitted online. People can do this on the page Comment on Proposed Regulations and Submit Petitions. A variety of search options lead to the document required. The direct link to the relevant section of the Federal Register is also located here. People who want to submit comments must follow the instructions to the letter.