OK so this post is assuming that you have competed first draft of your book. It is going to take you through the next few steps that you need to take to move your first draft into a better book.
Get a hard copy (printed) version of your book in your hands. Yes. Paper.
You are going to print your entire manuscript out (MS), single-sided and get it bound or stapled. Do this at a printer and get them to bind it with a plastic ring binder and put a clear plastic cover on it. Make sure you have page numbers on your MS.
Never do a read-through or edit on your screen - this will NOT work and is a totally different brain process.
Sit down and read your entire book from start to finish ONCE. You need to do this read-through once, and do it thoroughly. There is a limit to how many times you can read your own work. Your single task is to focus on making all the notes that you are going to action over the next few weeks.
Your biggest challenge?
This is going to be to STOP YOURSELF from making ANY of these changes on your typed manuscript. Whatever you do, DO NOT dash to your computer and try and fix any problems until you have read the entire thing and followed all the steps. You will try and fix something in Ch. 3 that may have no relevance to the overall story arc.
What are you doing as you do the read-through?
If you had a manuscript appraisal or a beta reader (depending if you are on a mentorship / bootcamp that facilitates that buddy process) you are also going to incorporate possible buddy notes into your rewrite so wait for those. You will notice if you get a MS appraisal that the appraisal is a separate document (not edits on your text). It is high-level and asks you to fix / rewrite at that level. The small stuff we leave till later.
Read. Think. Make notes.
Then edit like a surgeon.