Personally, I stay motivated a couple of ways:
1) I have a post about my Yusupov progress that I update every time I finish another chapter. Feel free to post your progress in my post, or create your own. I also keep a blog and update my progress there.
2) I don't just play a ton of blitz and bullet here on the site. I spend the majority of my time playing longer games against my computer and at club. Seeing progress in how I am doing at that keeps me motivated to keep doing Yusupov. If I depended on progress at blitz I would have quit. My blitz is horrible and has stayed horrible. I'm much stronger at longer time limits.
3) I try to actively incorporate some of his ideas into my game. For example, I have switched to using his way of counting material. That makes me much more likely to sac the exchange if I can get a pawn too since 4.5 does not compare all that badly to 3+1. Likewise his ideas on centralization are something that can be incorporated into games very frequently.
4) I try to maintain a pretty regular pace, with a chapter every week (most often) or occasionally two. I don't try to do more than that as the time commitment to do this right is large. And I have other chess related study I want to do as well (like tactics every day).
I do absolutely recommend approaching the book the way he says to do it. I have a database, and I actually do enter the positions into my database for easy review. But I find the material much more instructive and beneficial actually setting the positions up on a board, writing my lines out in a notebook, etc.
How easy or hard the material is, will vary. First because some of the material is harder than others. But also because of how much we already know. For example, I have been doing lots of tactics puzzles, so I tend to find the chapters dealing with tactics easier than the chapters dealing with positional ideas. When you find a tactic, it either works or doesn't (of course you might overlook key lines). But with positional ideas, it can be more subtle and more difficult to know if you have found the right line.
I have to come to the place where I'm OK knowing I'm not going to Ace every chapter. That is all right.
I have boost your chess vol 1 as well as build up your chess vol 2 and chess evolution mastery vol 3.
But I find most of the chapters either easy or too difficult.
Can someone recommend me how to stay motivated?