Step 1: Stomp around the house, kick things (inanimate things only!) scream that your commenter is insane or stupid or both. Go for a beer. Do NOT email your commenter at this time. Especially if he or she is an editor who has purchased and is paying for your work. Especially after you have had the beer.
Step 2: Thank the commenter. Usually via email. Be brief, be upbeat, be happy. This person has taken the time to try to help you make the manuscript better. Trust that this individual has your best interests, and those of your work, at heart. Sometimes, this is very, very difficult. But it is usually also true. Do NOT respond to the comments at this time. Especially if you have not yet fully completed step 1.
Step 3: Do something productive with the fretful energy of the pending changes and of your reaction to them. Take a walk, ride your bike, plant a flower, watch an absurd video on YouTube. Anything that helps you relax. Note: this may suggest a return to Step 1 if you relax by kicking things.
Step 4: Read the notes carefully. Perhaps you have read them prior to Step 1. That’s fine, but you still need to read them after Step 3. If this prompts a desire to return to Step 1, feel free.
Step 5: If you have received the notes old-style (on paper) or in a separate document from the work, it helps to snip the relevant sections and stick them where they belong in the context of the work. Note: the physical act of snipping the comments can result in a more complete experience of Step 1. By all means, indulge. But not with your only copy.
Step 6: Accept that some of your deathless prose indeed must die. (Step 1, etc).
Step 7: If you have questions or concerns about how to apply the comments, and you have recourse to the commenter, ask for guidance and clarification. If you have an agent, he or she may also be a valuable resource in understanding what is being asked of you. Depending on reply, repeat Steps 1, 2 and/or 3 as needed.
Step 8: Look for any overarching criticism that will affect the structure, conception or central direction of the work. This is where you need to begin. I know, you’d like to handle capitalizing all the names properly or some other small thing with which you totally agree. But really, that’s just re-arranging the deck chairs, don’t you think?
Step 9: If you need to take parts of the work back to the proverbial drawing board as a result of your Step 8 analysis, do so now. We’ll wait.
Step 10: Look for any criticisms that center on issues of character development. These may affect plot or conception (as in Step 8), but are often more pervasive than any one scene. Thankfully, they can also be dealt with as you proceed through the manuscript, keeping in mind the need to revamp that character as you go. You may find you are tweaking only a few words, but that those new words will sketch the character in a whole new way.
Step 11: If any specific scenes or moments have been noted, go to them directly and see what can be done for them. If the answer is nothing, remind yourself of Step 6: Some of your deathless prose must die. This is especially key if you have been asked to trim for length.
Step 12: Begin at the beginning and work until you reach the end. Make any small changes you come across and view the new scenes or structural changes in context to smooth transitions and remove references to things that no longer exist. If you’re not sure how to handle a comment, make a note of where it is and what it pertains to, then keep going forward. Repeat as needed.