I think that self help books are overrated. The best book to read is one that challenges you or one that inspires you, like a good work of fiction.
All the books which are about the concept of Ikigai. It's a very simple thing, but it can mean something huge for us. In a broad way, Ikigai is why you wake up in the morning, what it is the engine that helps you to go on.
Any kind of poetry is good for self-help. I'm alwaus reading different books, but comong back to some of them. Currently is "Black Roses" from Simom Armitage and "Today I wrote Nothing" from one of the greatest Russian authots Daniil Kharms.