Some useful things to comment on would be:
- specific information about how the reader was useful for you
- ideas for using the reader in conjunction with a specific textbook or classroom activity
- questions about the grammar and/or vocabulary of the reader
- typos or other errors that you see in the reader which need to be corrected
- concerns about content (readers can be flagged as "caution" if there are themes or images that are violent or otherwise not suitable for all readers)
If you are having trouble finding the right page, you can also just leave a comment in reply to this post - but if you do that, make sure you include the title of the reader you are commenting on, plus its address, so we can match up your comments to the reader.
Thanks for your input! By sharing ideas about what makes readers really useful, we can all learn to do a better job, both in creating the readers and in using them ourselves.