To be able to answer you, my reader friend, you have to be clear that self-improvement has different parameters or if you prefer different degrees. Thus, self-improvement in life practices a level social, professional, family y sentimental where the mind is the flow of knowledge and necessary protagonist has its great representative books to acquire that knowledge of oneself even at a social and practical level. But the spiritual parameter that goes from the why of your emotions… The constructive and the destructive ones, your feelings of connection with other human beings, of your capacity for empathy and understanding and loss of fears to unlock good judgement. Your ability to connect with your experiences even beyond this life… This parameter also has its great books. Finally we have those few books that add both parameters and that to understand them 100 percent you have to have traveled a long road of search, and if you can help you with these great books to achieve self-improvement.
If you are interested in self-improvement on a social and practical level I would read:
“Your Wrong Zones” by Wayne Dyer –EXCEPTIONAL.
“Emotional Intelligence” Daniel Goleman. –UNIQUE
“Think and Grow Rich” Napoleon Hill – DEVELOPER
If you are interested in self-improvement on an emotional-spiritual level:
“God comes back on a Harley” Joan Brady –AWAKENING
“Initiation”. Elisabeth Haich . –ENLIGHTEN YOURSELF
“The Chosen Ones” Margarita Arnal Moscardo –AUTHENTIC
There are many great books that I haven’t mentioned but I think these are a great guide to self-improvement and will be of great use to you.