You can also download the Wim Hof app for free, which has a feature to guide you through the breathing exercise in a more personalized way.
If I said anything has a pronounced effect on sleep restfulness or concentration it's been whole plant based food which I tried incorporating in my diet more after watching Forks over Knives.
I still eat the occasional meat and cheese, but I found especially useful to replace dinner with WPBF. I naturally, i.e. without alarm, wake up after 6-7h of sleep instead of 9-10h, and I feel much more awake during the day.
I think it's mostly that if you eat heavy (greasy, meaty, cheesy) food in the evening your digestive system is so busy you can't sleep properly.
I would say the effect is much larger than cutting out alcohol, even though that's of course also helpful.
IMO both of these are better integrated with pranayam.
I don't know about Wim Hof but I hope that he preserves the spirit and the ambience of yoga while imparting the knowledge and also cites references and gives credit where it is due. Yoga works on a much deeper level than just curing ADHD if done in the right ambience. Even a moderate yoga practitioner raises and expands their consciousness from oneself to being coextensive with everyone and everything.
You're better going straight to the source: http://www.yogebooks.com/english/atkinson/1903sciencebreath....
Thats probably the reason why the author of this comment feels that it is far better going to the source rather than cherry picking a few practices.
Learning the Wim Hof breathing method changed my life for the better. And this is not meant as an advertisement for his business; you can find the same technique (with or without branding) for free everywhere online. I highly, highly recommend trying it out.
Whenever I feel scatter-brained, lack focus or creativity, when I'm feeling down, (or just feel like it) ... this is my go-to method. ~20 minutes of controlled, intermittent hypoxia. Not to mention it's an excellent "tool" to have in psychologically and/or physically stressful times, such as after an accident and being in a hospital (speaking from experience).