Start with high-confidence affirmations & mantras books, then narrow by subgenre or adjacent topics.
Stake Your Claim
Emmet Fox
The Game of Life and How to Play It
Florence Scovel Shinn
Your Word Is Your Wand
The Power of the Spoken Word
Florence Scovel-Shinn
Attaining Your Desires
Geneviève Behrend
The Amazing Secrets of the Yogi
Charles F. Haanel
How to Live Life and Love It
The Magic Word
Robert Collier
Thoughts Are Things
Prentice Mulford
Words to Live by
Jade Purple Brown
As a Man Thinketh & the Way of Peace
James Allen
Your Invisible Power and How to Use It