I'm in the process of editing and completing the final draft of Seeker of Legends, the second book in the Fate of Legends series (for a preview, click here).
To edit my first drafts, I print them out, 2 pages on a side, double-sided. I hole-punch them and put the book in a three-ring binder, and go through it with a red or blue pen, making changes and additions as I go. When I'm done, I make these edits on the word document.
I usually do this process 2-3 times, sometimes reading the book backward (from the end). Each time, I make a few thousands changes, and do a complete spelling and grammar check afterward. The process takes a month-and-a-half to two months. It's a lot harder than hiring an editor, but also much cheaper!
One day, I might hire an editor, if it becomes cost-effective to do so. But with books over 150,000 words, it can get awfully expensive.
That being said, if you find an error in one of my books, feel free to let me know at firstname.lastname@example.org. If I agree it's a mistake, I'll gift you one of my books!