There are many books on the topic of Zen Archery (a few of them are good, a lot of them are actually horrible). One of the books I recommend the most on this topic are "Zen Bow, Zen Arrow", which includes a biography and the poems of Awa Kenzo - it is the poetry that is most useful and profound if you want to get into zen archery and want to understand the essence of Zen Archery.
Another book I recommend is "The Unfettered Mind", which is actually not an archery book. It is a series of letters written by Takuan Soho and sent to famous samurai approx. 500 years ago, during which he advises them on matters of concentration, swordplay and politics. But the advice he gives in the letters doesn't just apply to swordsmanship, it also applies to archery and many other tasks.
The last book I recommend is "Kyudo - The Essence and Practice of Japanese Archery" by Hideharu Onuma. This book is for people who want to get into the ceremonial practice of Kyudo and aren't really into Zen Archery. But if your focus is on doing both Kyudo and Zen Archery, then I do recommend that particular book for your collection.
Now you might think "Hey, what about 'Zen in the Art of Archery' by Eugen Herrigel. Honestly. I read it. I was not impressed with his writing and I find he presents a stereotype of the practice of Zen within archery. You can still read the book if you wish, but I recommend you not put too much stock in his writing.
There is a video below about 'archery meditation' made by an instructor at a tropical resort, and the video gives you an idea of the concentration required to do archery - but it really is only the tip of the iceberg. I have created a list of fifteen tips further below for people who want to improve their concentration skills for the purposes of archery.
15 Concentration Tips for Archery
#1. Do things slowly and methodically. Not just archery, but everything you do. eg. Wash the dishes slowly and methodically and concentrate on what you are doing as you do it slowly.
#2. Eat foods that take a long time to eat. Fruits like apples and bananas for example can be eaten slowly (don't cut them into smaller pieces, that is just speeding up the process).
#3. Do one thing at a time. Avoid multitasking.
#4. Focus your eyes on what you are doing. Don't look at the archery target until you have completed each step.
#5. When do focus on your target, focus your eye at a single point in space.
#6. Take your time aiming.
#7. Avoid speed shooting. This is not a speed competition. You should not be looking at the clock, counting the seconds or even worried about how much time you are spending on the shot.
#8. Do math in your head. The more complicated math you can do in your head, the more you have to concentrate and remember what you are doing. Focus on the math. Visualize it.
#9. Ignore emails, texts and don't listen to music unless you have set aside a specific time of day just for listening to music, answering emails or texts. Focus on only one of these things at once.
#10. Motivate yourself on what you are doing. Whatever you are doing is important, otherwise you would not be doing it. Focus on the task, stay motivated as to why you are doing, why you want it to be perfect. It doesn't matter what you are doing, regardless of whether you are grilling bacon (so fatty, but it serves my example because if you lose concentration and burn the bacon you will realize you were distracted) or composing an email (and then have typos or poor grammar in sentences).
#11. Plan what you are doing before you do it. Have everything ready and set in place, ready to be put in motion.
#12. Shut the door, turn off the radio, close the window (to avoid noise from the street) - shut out all distractions from what you are focused on. So if you are listening to an audiobook, that should be the only thing you are listening to - and focusing on listening should be the only thing you are doing.
#13. Don't forget to take breaks. Eventually your mind gets exhausted and you just to relax and unwind. Time to watch or listen something entertaining, spend time with family or even just take a nap. People can't concentrate if they are tired or mentally exhausted.
#14. Eat, but don't overeat. Being hungry is a distraction, but so is gastric distress and heartburn.
#15. Slow down when making important decisions. Sometimes this is necessary. A hasty decision made when you haven't concentrated on the consequences isn't going to help you. With archery this means you need to think about your next shot before you even do it. Know where you want to be aiming, use your best judgement based on the distance and all your knowledge. Your first instinct is rarely correct, but you don't want to over-think it either.