TL;DR - sleep properly, eat properly, exercise regularly, and learn to live in the present.
I learned to calm my mind by reading, and following the exercises in a series of books called, 'The power of now', and 'Practicing the power of now' by Eckhart Tolle. Some people have difficulty in picking up these books, particularly 'The power of now', because it was featured on Opera. Or because it's a'new age' title. If this is you (dear reader): get over yourself, and this book will change your life. It's a tiny book that you can read, cover to cover, in a few hours. It's available in many languages, and also as an audio book.
These books will teach you how to calm your mind by learning to be 'present'. You'll learn how to observe your mind -- how to accept the thoughts, obsessions, preoccupations about things that happened in the past; how to accept the worry, dread, and anxiety about things that may happen in the future. Past and future are important, but none truly affect you like the present. Right now, right this very moment as you read what I've typed, you are actually free of these burdens.
Learning to be present was foundational to everything else I've done to break out of the cycle. I became self-aware in a way that made it impossible to reconcile the various negative character traits I had developed from early adolescence. I stopped procrastinating not because I developed some super-human will power or laser-like focus, but because I learned to spot the moment my mind wandered away from the task at hand. I stopped waiting for things to be 'perfect' before starting something because, in the present, nothing is perfect or imperfect -- it just is what it is and that's that. I stopped waiting for things to fall into my lap (to get lucky) because, for the first time that I can remember, things started happening because I made them happen.
We'll call this Phase 1, from about 2012 to 2016. The problem is that over time I became complacent. I got used to the new 'normal'. I started using 'being present' as a band-aid, a life-hack that I could apply whenever I noticed I was going back to my old ways. I was also increasingly feeling tired and lacking mental and physical stamina; finding it difficult to stay sharp and focused in meetings, particularly in the afternoon. It got to the point where all those old problems -- procrastination, depression, anxiety -- were becoming more and more difficult to manage simply by being present. The problem: I was overweight, and likely suffering the effects of early type 2 diabetes; the effects of drinking soda with every meal, eating four or five meals a day, and limiting my physical exertions to getting on and off the bus to work.
This is when I discovered intermittent fasting, the Keto diet and regular exercise.
Phase 2, from about 2016 to the present. I bought a bicycle and started cycling to and from work (12 miles round trip). I stopped eating breakfast and lunch. I stopped drinking soda, and eating sweets. I reduced my carb intake to 5g a day. Within about a week, I had lost 3% weight. In the first month, I lost 8%. After three months, I was 15% lighter. I started sleeping better -- a LOT better -- and waking up effortlessly in the morning. I had never been a 'morning person', and used to set four or five alarms (and a dozen snoozes); now I don't even set an alarm. I can't help waking up early and feeling completely refreshed! I started wearing clothes that fit well -- this is an underrated, AMAZING feeling! At work, I stopped feeling tired at all; in fact, I was (and still am, almost to the annoyance of my colleagues) sharp and focused throughout the day.
> Did I do anything in particular to break out of the cycle?
If you're looking to begin, I would start all of the above at the same time. It's going to take a few months to really get going, but you'll feel the benefits almost immediately (certainly within the first week). After about a year, you will hardly recognise the person you used to be!
Good luck, and godspeed.