how to come up with good title for book?

Most authors work with two titles: their working title when they start writing, and the ultimate title they arrive at when they finish the book. Sometimes it is even the editor or publisher who comes up with the title.

So don't fret, just write and let the muse take you where she shall.

The title will make itself known in its own good time!

well my mom is a writer and she usually will write the entire story then come up with the title after, like let the story name itself.. also having a play on words that hints to the overall feeling of the book is always an interesting title... but simple and short is good too

A lot of books I have read take tiny details from a book that matter a whole lot and turn that into the title.