Well for starters Thich Naht Hanh has written a lot of books. Personally my next recommendation would be No Mud, No Lotus. There is a fair amount of conceptual overlap between his books, so it's probably not necessary to read every book he's written unless you find his specific philosophy compelling and want to emulate it.
I think of Being Peace as a good entry point for a person looking to change their mindset, a sort of reset. It's good guidance for getting some control of the emotional noise of daily life, especially anxiety, fear and anger.
A good next step is Getting to Where You Are by Steven Harrison. This has practical guidance for regular meditation as a practice, without any of the mysticism. It is a signpost on the path to self-regulation and self-acceptance (but I think not the best starting point if you don't already have some grounding in mindfulness and meditation).
After the others, I think Journey Without Goal by Chögyam Trungpa is worthwhile. This one does lean heavily on the religious background of its philosophy, and I think it's necessary for the reader to know what they're looking for while reading it, to understand the mythology as allegory. The value of this book is in changing your concept of how life might be lived entirely, a sort-of restructuring of your perspective on existence and your path through it. I don't think it should be jumped into without an established foundation of meditation practice. Frankly, if you haven't already established patience within yourself and built that place of internal calm, and taken at least some steps toward self-understanding and self-acceptance, this won't do you any good. I think it's important to note that in spite of the title, some people heard this message and believed that it was a pathway to enlightment as some sort of end goal. No such thing is promised, and if you go into it expecting that you will get lost.
So yeah,
- Being Peace - find calm, and begin meditation practice
- Getting to Where You Are - self-acceptance, and refine your meditation
- Journey Without Goal - self-knowledge, and looking forward
...in that order.
Some other books I'd recommend which kind of extend these ideas:
- Rules For A Knight by Ethan Hawke
- The Analects (of Confucius)
- Quiet: The Power of Introverts in a World That Can't Stop Talking by Susan Cain
- Tao Te Ching by Lao Tsu


These people are cartoon villains.