Personal Development Book Recommendations

OP, I don't want to hijack the thread so if you'd rather I just PM this to Pierogi, I'll delete and send to him, I just think this could be helpful to others. I'll give you some theoretical/anecdotal stuff first, then get into tactics of what specifically I do

one of the reasons why I loved 7 habits so much is because of the 2nd habit "begin with the end in mind," now perhaps you already do this since you follow stoic teachings but I found covey before I found aurelius, epictetus, seneca, and frankl, so this idea of writing your own eulogy (I believe he recommends you do this) was a bit startling to me, but since I was feeling lost at the time in my life when I found covey, I did it. I wrote my own eulogy, and it forced me to think about how I want others to see me on the one hand, but the most important thing it taught me was what was really important to me. what did I want to be remembered for?

this also led me to one of my ongoing thought experiments, where I envision myself on my deathbed, in my final moments, doing an accounting of my life. what will I wish I had done more of? what will not be on my mind at all? what am I likely to be glad that I did? all of this is to say that you MUST MUST MUST identify what is truly important to YOU. I cannot tell you what your priorities are, so realize that once you begin this reflection process, you may change or course correct (another reason why I say check in every so often), but the basic core of your priorities should be relatively fixed over time absent some existential crisis.

the other thing I've noticed is that while lists are great ways to get things done from day to day, they're awful at helping you see the big picture, so I lean towards more of a narrative style, another thing I learned from covey's 2nd habit (eulogies are very different from resumes), which I believe is helpful because many of the mental traps I found myself in where when I was failing to shut down all of the distractions of everyday life. forcing myself to no multitask by sitting with a blank sheet of paper and a pen (and usually a cocktail) allowed me to think more deeply and dream a little more which I believe helps, as goal setting should not only be practical, but also creative.

additionally, as your life evolves, you will course correct and certain things that were once big priorities may have waned or bubbled towards the top, so self reflection is super important and I'd recommend you do it consistently (I usually check in on the bigger stuff twice a year). this leads into how to keep the motivation going. I'm dubious of willpower, I believe it plays a part, but just like I don't think all of success is neither hard work nor luck, nor is all of self improvement willpower, you need to have systems. it's a lot easier to continue on a course if you have already affirmed it's a priority, because while you're doing some of the tactical stuff it's easy to say "why the fuck am I doing this again?" but when you remember it's tied to a bigger purpose, it's easy to keep going. on the flip side, if you set out for a goal and then when you check in with yourself you find you're not doing it, you can reflect on it and more likely than not, one of two things is happening - either it's not truly a priority and you should stop, or you have not sufficiently eliminated enough other bullshit from your life to allow the space to accomplish said goal.

so here it goes

1. write out a narrative of what I want my life to look like in 1, 5, and 10 years (most focus on the 5 & 10 year timeframes), this should take up about a half a page on a word doc single spaced 11-12pt font (each time frame, maybe not the 1y one though). to help guide your focus, address all of the 6 spokes of life - spiritual/ethical, social/cultural, career/financial, mental/educational, family/home, and physical/health. some questions that can help this could be like the following
   1. what's more important to me? travelling my ass off or saving for a large purchase?
   2. do I need a graduate degree/advanced certification to get where I want to be?
   3. do I want to be married? with kids? without kids? pets? where do I want to live? urban, suburban, rural, or nomadic?
   4. how's my mental health, spirituality?
   5. what are my physical/health goals? if you're not in good shape, what's a reasonable accomplishment within this timeframe? if you're already in shape, what's the priority, maintenance? improving flexibility because you're already strong? improving endurance because you're already powerful? improving strength because you're already a marathon runner? improving diet because your early 20s metabolism is starting to show signs of wear?
2. read, re-read, edit, and then read and re-read again the narratives from step 1, see what the common threads are. what do you keep bringing up over and over again? what were some ideas that were swirling around in your head that you thought might have been important but really aren't? (hint: I put this stuff on my bucket list. for example, I'd love to see maccu picchu and learn piano but they're not near term priorities)
3. of the stuff that seemed to bubble towards the top of your list from #2, pull on each one of those threads individually. ask yourself: why has this not happened yet? how can I accomplish this? is this a reasonable goal within this timeframe?
   1. why has this not happened yet? I only say this because there may be some underlying psychological issues you need to fix before you can do something as daring as say starting your own business. maybe you have undiagnosed depression, maybe you have poor self esteem issues, etc., and those are far more important than developing a business plan
   2. how can I accomplish this? GET VERY SPECIFIC. if your goal is to get a job in a certain industry, outline all of the job requirements you'll need, how many people you will need to network with, how long it will take to contact them, how many jobs are available in said industry (also handy during this part is having a side list where you mark down things you need to research more). if your goal is physical like weight loss, how much time do you have every day to work out, what types of workouts do you enjoy, how consistently can you do it, what do you eat/drink on a daily basis that needs to be tweaked? from this step, you will begin to create the outline of the systems that help you achieve what's important to you. focus here should be on regular (daily, weekly) tactics you can employ
   3. since asking if the goal is reasonable in that timeframe is obvious (either yes or no), another tool I use here is via negativa. back to #3.1, often times the reason I haven't done something is because I haven't eliminated enough shit from my life to actually do it. whether that's eliminating useless expenses preventing me from saving $ for travel, eliminating bad friendships to make the space to deepen good ones, eliminating social media/wasted internet time to allow space to learn language, whatever. I take a slash and burn approach when I want to introduce something new, and I suggest the same for everyone. you quite literally cannot do it all, so you must eliminate some stuff, this is a central pillar of my system and the systems that will allow you space to achieve it.
   4. re-write your routine to incorporate some of the stuff from 3.2, and then just do it. this will require you to get outside of your comfort zone, but I find this is easier if you approach it not only with a well-thought out plan, but also because you're focused on your priorities, not what society thinks should be a priority
4. 6-12 months later (or more often if motivation is hard for you), check in with yourself and ask the same questions you asked yourself in step 3. if you still have motivational issues, here's what I'd do
   1. tell others about your goals and ask them for advice. maybe you already know someone who's lost a lot of weight, or has that PE job you want, or speaks that language, or has trained for triathlons. stay in touch with them regularly, they have to put forth very little effort to help and you will feel an intrinsic pull to live up to what you promised them
   2. kitchen sink approach - try something and see if it sticks. for me, myfitnesspal was good when I needed to change my diet, for others something like a calorie counter, whole30, etc., works. for fitness sometimes people make bets against their friends, or use myzone/whoop/strava, just try stuff and see what works. if you have trouble staying motivated, it's because you don't know what motivates you, so you will need to have trial and error until the habit sticks. 
   3. change it up - the first time I tried to become a runner, I did it in the morning because that's what cam hanes did and everybody else I talked to. I'm a morning person, but not a morning exercise person (unless it's surfing or it's the only time I have that day). I found much more success in running before lunch or at the end of the day, sometimes a simple change can make all the difference.

 so there it is. full disclosure, when you begin on this journey, it will take years to see large progress, but only months to see noticeable progress, so keep the faith. plus, I've noticed that because you spend so much time focusing on what you care about, it doesn't feel as much like studying for the SAT or some other shit that you HAVE to do

happy to clarify anything or answer follow ups if needed

EDIT - didn't address your friends' sudden lifestyle changes. to me this seems like he's approaching self improvement backwards, going with tactics before strategy (short term before long term), hoping that one thing or another will be the magic formula, I say bullshit. if he wants to cut down on his inflammation and improve overall health and relationship with alcohol and one of the ways to do that is to favor wine over beer, fine, but it really depends on how he got to that tactic that matters I believe, because if it turns out that changing to wine didn't solve anything, what does he have to fall back on? nothing! no principle he can go back to, he's just lost again. ditto for the toe shoe thing - what's the overarching goal? so I guess I'd say good for him for trying to improve himself, he's doing more than 99% of the population I'd guess (most people I meet are NOT on the path), I would advise him to sharpen the saw by zooming out to see the bigger picture, and put strategy/long term goals ahead of tactics