Here is the link to the ebook: https://7website.github.io/ebook/
I find UX and UI design to be very important in attracting customers. In college, I took a course called Human Computer Interraction (HCI). This HCI course deals with how best we can make user experience and interraction with technology easy and successful.
I applied the knowledge I took from this course to my apps that I built later on.
However, there are blogposts and articles written on this topic ,
these great resources are available on the internet, and I compiled most of the links to these resources in an ebook.
I f you interested, you could buy and read in your spare time. Thanks